Management's discussion and analysis reviews our consolidated financial position at December 31, 2017 and 2016, and our consolidated results of operations for the three years in the period ended December 31, 2017, and where appropriate, factors that may affect future financial performance. This analysis should be read in conjunction with our audited consolidated financial statements, notes thereto and selected consolidated financial data appearing elsewhere in this report.
All statements, trend analyses and other information contained in this report and elsewhere (such as in filings by us with the SEC, press releases, presentations by us or our management or oral statements) relative to markets for our products and trends in our operations or financial results, as well as other statements including words such as "anticipate", "believe", "plan", "estimate", "expect", "intend" and other similar expressions, constitute forward-looking statements. We caution that these statements may and often do vary from actual results and the differences between these statements and actual results can be material. Accordingly, we cannot assure you that actual results will not differ materially from those expressed or implied by the forward-looking statements. Factors that could contribute to these differences include, among other things:
The economic and personal investing environments continued to be conducive for high sales levels as retirees and others look to put their money in instruments that will protect their principal and provide them with consistent cash flow sources in their retirement years. However, our sales slowed in the last half of 2016 and throughout 2017 due to continued competitive pressures within each of our distribution channels and an industry wide slowdown in fixed index annuity sales. We continue to face headwinds from low interest rates, strong equity markets and the DOL conflict of interest fiduciary rule.
We specialize in the sale of individual annuities (primarily fixed index deferred annuities). Under U.S. generally accepted accounting principles ("GAAP"), premium collections for deferred annuities are reported as deposit liabilities instead of as revenues. Similarly, cash payments to policyholders are reported as decreases in the liabilities for policyholder account balances and not as expenses. Sources of revenues for products accounted for as deposit liabilities are net investment income, surrender charges assessed against policy withdrawals and fees deducted from policyholder account balances for lifetime income benefit riders, net realized gains (losses) on investments and changes in fair value of derivatives. Components of expenses for products accounted for as deposit liabilities are interest sensitive and index product benefits (primarily interest credited to account balances and changes in lifetime income benefit rider reserves), changes in fair value of embedded derivatives, amortization of deferred sales inducements and deferred policy acquisition costs, other operating costs and expenses and income taxes.
Our business model contemplates continued growth in invested assets and non-GAAP operating income while maintaining a high quality investment portfolio that will not experience significant losses from impairments of invested assets. We are committed to maintaining a high quality investment portfolio with limited exposure to below investment grade securities and other riskier assets. Growth in invested assets is predicated on a continuation of our high sales achievements of the last five years while at the same time maintaining a high level of retention of the funds received. The economic and personal investing environments continued to be conducive for high sales levels as retirees and others look to put their money in instruments that will protect their principal and provide them with consistent cash flow sources in their retirement years. However, our sales have slowed since the first half of 2016 as competition in our distribution channels escalated, rates from several of our competitors were appreciably above prior levels, and there continues to be uncertainty regarding the DOL conflict of interest fiduciary rule.
The cost of money for fixed index annuities and average crediting rates for fixed rate annuities are computed based upon policyholder account balances and do not include the impact of amortization of deferred sales inducements. See Critical Accounting Policies-Deferred Policy Acquisition Costs and Deferred Sales Inducements. With respect to our fixed index annuities, the cost of money includes the average crediting rate on amounts allocated to the fixed rate strategy, expenses we incur to fund the annual index credits and where applicable, minimum guaranteed interest credited. Proceeds received upon expiration or early termination of call options purchased to fund annual index credits are recorded as part of the change in fair value of derivatives, and are largely offset by an expense for interest credited to annuity policyholder account balances. See Critical Accounting Policies - Policy Liabilities for Fixed Index Annuities and Financial Condition - Derivative Instruments.
We are currently in the midst of an unprecedented period of low interest rates and low yields for investments with the credit quality we prefer which presents a strong headwind to achieving our target rate for investment spread. In response to this persistent low interest rate environment, we have been reducing policyholder crediting rates for new annuities and existing annuities since the fourth quarter of 2011 and starting in 2017 have begun focusing on investments with less liquidity that provide higher yields and have a track record of positive credit performance over time. Spread results for the 2017 and 2016 periods reflect the benefits from these actions. We continue to have flexibility to reduce our crediting rates if necessary and could decrease our cost of money by approximately 49 basis points if we reduce current rates to guaranteed minimums. Investment yields available to us in 2017 increased compared to 2016, however they remain below our portfolio rate. Investment yields at these levels will continue to put downward pressure on our investment spread and product returns.
Net income, in general, has been positively impacted by the growth in the volume of business in force and the investment spread earned on this business. The average amount of annuity account balances outstanding (net of annuity liabilities ceded under coinsurance agreements) increased 8% to $46.8 billion for the year ended December 31, 2017 compared to $43.5 billion in 2016 and 14% for the year ended December 31, 2016 compared to $38.1 billion in 2015. Our investment spread measured in dollars was $1.2 billion, $1.0 billion, and $924.8 million for the years ended December 31, 2017, 2016 and 2015, respectively. As previously mentioned, our investment spread has been negatively impacted by the extended low interest rate environment (see Net investment income).
Net income for the year ended December 31, 2017 was negatively impacted by $35.9 million related to the revaluation of our net deferred tax assets using the newly enacted federal tax rate as a result of the Tax Cuts and Jobs Act of 2017.
The unlocking adjustments in 2017 decreased amortization of deferred policy acquisition costs by $48.2 million and amortization of deferred sales inducements by $34.3 million. During the third quarter of 2017, the most significant revisions to such assumptions were account balance true-ups which were favorable to us due to stronger index credits than we assumed due to strong equity market performance and adjustments to generally decrease lapse rate assumptions to reflect better persistency experienced than assumed. The favorable impact of the account balance true-ups and lapse rate assumption changes was partially offset by reductions in estimated future gross profits attributable to revisions to assumptions used in determining reserves held for lifetime income benefit riders as well as an increase in estimated expenses associated with a reinsurance agreement with an unaffiliated reinsurer.
The unlocking adjustments in 2015 decreased amortization of deferred policy acquisition costs by $11.0 million and amortization of deferred sales inducements by $5.6 million and included the impact of account balance true-ups as of September 30, 2015, which were favorable to us due to stronger equity market performance than we assumed, favorable adjustments to lapse assumptions to reflect better persistency experienced than assumed and unfavorable adjustments to investment spread to reflect lower spreads being earned than assumed. The favorable impact of the account balance true-up and lapse assumption change was largely offset by reductions in estimated future gross profits attributable to revisions to assumptions used in determining reserves held for lifetime income benefit riders.
The 2017, 2016 and 2015 revisions to reserves for lifetime income benefit riders were consistent with unlocking for deferred policy acquisition costs and deferred sales inducements described above. The 2017 revisions were primarily due to the lapse rate assumption changes described above and changes to our account value growth projections. The 2016 revisions were primarily due to actual index credits on policies being lower than projected over the past four quarters. The most significant assumption change generating the 2015 negative impact on net income was an increase to the primary election age to begin receiving lifetime income from 67 to 70 as our experience has shown that age 70 is the most popular age at which policyholders elect to begin receiving lifetime income benefit payments. The lifetime income benefit payments are determined by applying a payout factor to the rider's benefit base. The payout factors vary by the age at the time the lifetime income is elected. In early versions of the rider, the age band for payout factors was 10 years (i.e. 60-69; 70-79). As a result, policyholders have an incentive to defer their lifetime income election until age 70, when the payout factor stepped up. Subsequent versions of the rider reduced the age bands between payout factors to five years and the rider we currently sell has a different payout factor for every age. With these structures, assumption revisions from any further developments in our experience for primary election age should have a smaller impact than what was experienced in 2015.
Non-GAAP operating income, a non-GAAP financial measure (see reconciliation to net income in Item 6. Selected Consolidated Financial Data) increased 133% to $285.1 million in 2017 and decreased 38% to $122.3 million in 2016 from $195.8 million in 2015.
The increases in annuity product charges were primarily attributable to increases in fees assessed for lifetime income benefit riders due to a larger volume of business in force subject to the fee and an increase in the average fees being charged due to higher fees on new products as compared to prior periods. See Interest sensitive and index product benefits below for corresponding expense recognized on lifetime income benefit riders. Surrender charges increased in 2017 and 2016 due to an increase in withdrawals from annuity policies subject to surrender charges as compared to prior years.
The decrease in yield earned on average invested assets in 2017, 2016 and 2015 was attributable to investment of new premiums and portfolio cash flows during those periods at rates below the overall portfolio yield. The average yield on fixed income securities purchased and commercial mortgage loans funded was 4.16%, 3.66% and 3.87% for the years ended December 31, 2017, 2016 and 2015, respectively. The average balance for cash and short-term investments was $0.2 billion, $0.9 billion and $0.3 billion in 2017, 2016 and 2015, respectively. The average yield on our cash and short-term investments was 0.55%, 0.05% and 0.07% in 2017, 2016 in 2015, respectively. The unfavorable impact from these items was offset by non-trendable investment income items which added eight, six and eight basis points to the average yield on invested assets in 2017, 2016 and 2015, respectively.
Change in fair value of derivatives consists of call options purchased to fund annual index credits on fixed index annuities, the 2015 notes hedges related to our 2015 notes and an interest rate swap and interest rate caps that hedge our floating rate subordinated debentures. The components of change in fair value of derivatives are as follows:
Our 2015 notes matured and were extinguished on September 15, 2015, and the 2015 notes hedges expired on that same date. The fair value of the 2015 notes hedges changed based upon changes in the price of our common stock, interest rates, stock price volatility, dividend yield and the time to expiration of the 2015 notes hedges. Similarly, the fair value of the conversion option obligation to the holders of the 2015 notes changed based upon these same factors and the conversion option obligation was accounted for as an embedded derivative liability with changes in fair value reported in the Change in fair value of embedded derivatives. The amount of the change in fair value of the 2015 notes hedges was typically equal to the amount of the change in the related embedded derivative liability and there typically was an offsetting expense in the change in fair value of embedded derivatives. See Note 5 to our audited consolidated financial statements for a discussion of the unwind agreements, the 2015 notes hedges and the 2015 notes embedded derivative conversion liability.
Net OTTI losses recognized in operations decreased to $4.6 million in 2017 and increased to $22.7 million in 2016 from $19.5 million in 2015. The impairments recognized in 2017 were primarily on a corporate security with exposure to the industrial sector in Latin America and additional impairments on previously impaired residential mortgage backed securities. The impairments recognized in 2016 were primarily on three corporate securities with exposure to the telecommunications, materials and energy sectors and two asset-backed securities with exposure to the energy sector. The impairments recognized in 2015 were primarily on two corporate securities with exposure to the metals and mining sector and one asset-backed security with exposure to the energy sector. See Financial Condition - Other Than Temporary Impairments and Note 3 to our audited consolidated financial statements for additional discussion of write downs of securities for other than temporary impairments.
The changes in index credits were attributable to changes in the level of appreciation of the underlying indices (see discussion above under Change in fair value of derivatives) and the amount of funds allocated by policyholders to the respective index options. Total proceeds received upon expiration of the call options purchased to fund the annual index credits were $1.6 billion, $272.3 million and $602.4 million for the years ended December 31, 2017, 2016 and 2015, respectively. The decrease in interest credited in 2017 was primarily due to a decrease in the average rate credited to the annuity liabilities outstanding receiving a fixed rate of interest. The increase in interest credited in 2016 was primarily due to an increase in the total account value of annuity liabilities outstanding receiving a fixed rate of interest. The average amount of annuity liabilities outstanding (net of annuity liabilities ceded under coinsurance agreements) increased 8% to $46.8 billion in 2017 and 14% to $43.5 billion in 2016 from $38.1 billion in 2015. The decrease in benefits recognized for lifetime income benefit riders in 2017 was due to the impact of revisions to assumptions used in determining reserves held for lifetime income benefit riders being less in 2017 than it was in 2016 which was partially offset by an increase in the number of policies with lifetime income benefit riders which correlates to the increase in fees discussed in Annuity product charges. The 2016 increase in benefits recognized for lifetime income benefit riders was due to increases in the number of policies with lifetime income benefit riders and correlates to the increase in fees discussed in Annuity product charges, and the impact of revisions to assumptions used in determining reserves held for lifetime income benefit riders. See Net income above for discussion of the impact of changes in the assumptions used in determining reserves for lifetime income benefit riders for the years ended December 31, 2017, 2016 and 2015.
Amortization of deferred sales inducements, in general, has been increasing each year due to growth in our annuity business and the deferral of sales inducements incurred with respect to sales of premium bonus annuity products. Bonus products represented 87%, 88% and 89% of our net annuity account values at December 31, 2017, 2016 and 2015, respectively. The increases in amortization from these factors have been affected by amortization associated with (1) fair value accounting for derivatives and embedded derivatives utilized in our fixed index annuity business, (2) net realized gains (losses) on investments and net OTTI losses recognized in operations and (3) changes in litigation reserves. Fair value accounting for derivatives and embedded derivatives utilized in our fixed index annuity business creates differences in the recognition of revenues and expenses from derivative instruments including the embedded derivative liabilities in our fixed index annuity contracts. The change in fair value of the embedded derivatives will not correspond to the change in fair value of the derivatives (purchased call options), because the purchased call options are one-year options while the options valued in the fair value of embedded derivatives cover the expected lives of the contracts which typically exceed ten years. Amortization of deferred sales inducements is summarized as follows:
See Net income and Non-GAAP operating income, a non-GAAP financial measure, above for discussion of the impact of unlocking on amortization of deferred sales inducements for the years ended December 31, 2017, 2016 and 2015. See Critical Accounting Policies-Deferred Policy Acquisition Costs and Deferred Sales Inducements.
Other operating costs and expenses increased 9% to $111.7 million in 2017 and increased 6% to $102.2 million in 2016 from $96.2 million in 2015 and are summarized as follows:
Salary and benefits expense increased in 2017 as compared to 2016 as a result of an increase in salary and benefits of $3.3 million due to an increased number of employees related to our growth, an increase of $3.7 million related to expense recognized under our short-term incentive compensation program and other bonus programs as a result of the short-term incentive compensation program being paid out at a higher percentage of target than in 2016 and an increase of $0.8 million related to a deferred compensation liability that is based on the value of our common stock. These increases were partially offset by a decrease of $3.2 million in expenses related to a retirement agreement with our former executive chairman.
The increases in reinsurance risk charges expense during 2017 and 2016 were due to the growth in our policyholder liabilities subject to a reinsurance agreement pursuant to which we cede excess regulatory reserves to an unaffiliated reinsurer. The increase in risk charge expense in 2017 due to growth in the policyholder liabilities subject to the reinsurance was partially offset by a lower risk charge percentage which was included in an October 1, 2016 amendment to the reinsurance agreement. The regulatory reserves ceded at December 31, 2017, 2016 and 2015 were $737.3 million, $638.1 million and $480.7 million, respectively.
Income tax expense and the resulting effective tax rate are based upon two components of income before income taxes ("pretax income") that are taxed at different tax rates. Life insurance income is generally taxed at an effective rate of approximately 35.6% reflecting the absence of state income taxes for substantially all of the states that the life insurance subsidiaries do business in. The income (loss) for the parent company and other non-life insurance subsidiaries (the "non-life insurance group") is generally taxed at an effective tax rate of 41.5% reflecting the combined federal / state income tax rates. The effective tax rates resulting from the combination of the income tax provisions for the life / non-life sources of income (loss) vary from year to year based primarily on the relative size of pretax income (loss) from the two sources.
For most of the bonds held in our portfolio the NAIC designation matches the NRSRO equivalent rating. However, for certain loan-backed and structured securities, as defined by the NAIC, the NAIC rating is not always equivalent to the NRSRO rating presented in the previous table. The NAIC has adopted revised rating methodologies for certain loan-backed and structured securities comprised of non-agency residential mortgage backed securities ("RMBS") and commercial mortgage backed securities ("CMBS"). The NAIC’s objective with the revised rating methodologies for these structured securities is to increase the accuracy in assessing expected losses and use the improved assessment to determine a more appropriate capital requirement for such structured securities. The revised methodologies reduce regulatory reliance on rating agencies and allow for greater regulatory input into the assumptions used to estimate expected losses from structured securities.
The use of this process by the SVO may result in certain non-agency RMBS and CMBS being assigned an NAIC designation that is higher than the equivalent NRSRO rating. The NAIC designations for non-agency RMBS and CMBS are based on security level expected losses as modeled by an independent third party (engaged by the NAIC) and the statutory carrying value of the security, including any purchase discounts or impairment charges previously recognized. Evaluation of non-agency RMBS and CMBS held by insurers using the NAIC rating methodologies is performed on an annual basis.
We hold fixed maturity securities with international exposure. As of December 31, 2017, 20% of the carrying value of our fixed maturity securities was comprised of corporate debt securities of issuers based outside of the United States and debt securities of foreign governments. Our investment professionals analyze each holding for credit risk by economic and other factors of each country and industry. The following table presents our international exposure in our fixed maturity portfolio by country or region:
At each balance sheet date, we identify invested assets which have characteristics (i.e. significant unrealized losses compared to amortized cost and industry trends) creating uncertainty as to our future assessment of an other than temporary impairment. As part of this assessment we review not only a change in current price relative to its amortized cost but the issuer's current credit rating and the probability of full recovery of principal based upon the issuer's financial strength. Specifically for corporate issues we evaluate the financial stability and quality of asset coverage for the securities relative to the term to maturity for the issues we own. A security which has a 25% or greater change in market price relative to its amortized cost and a possibility of a loss of principal will be included on a list which is referred to as our watch list. We exclude from this list securities with unrealized losses which are related to market movements in interest rates and which have no factors indicating that such unrealized losses may be other than temporary as we do not intend to sell these securities and it is more likely than not we will not have to sell these securities before a recovery is realized. In addition, we exclude our residential and commercial mortgage backed securities as we monitor all of our residential and commercial mortgage backed securities on a quarterly basis for changes in default rates, loss severities and expected cash flows for the purpose of assessing potential other than temporary impairments and related credit losses to be recognized in operations. At December 31, 2017, the amortized cost and fair value of securities on the watch list (all fixed maturity securities) are as follows:
Telecommunications: The decline in the value of this security is the result of regional economic recessionary pressure in Brazil and an increase in competition in the markets it operates. This issuer has seen weakened performance and heightened risk. We recognized an other than temporary impairment on this security during the first quarter of 2016 due to our evaluation of the operating performance and the credit worthiness of the issuer.
Several factors led us to believe that full recovery of amortized cost is not expected on the securities for which we recognized credit losses and reclassified OTTI from accumulated other comprehensive income to net income. A discussion of these factors, our policy and process to identify securities that could potentially have impairment that is other than temporary and a summary of OTTI is presented in Note 3 to our audited consolidated financial statements in this Form 10-K, which is incorporated by reference in this Item 7.
Our commercial mortgage loan portfolio consists of mortgage loans collateralized by the related properties and diversified as to property type, location and loan size. Our mortgage lending policies establish limits on the amount that can be loaned to one borrower and other criteria to attempt to reduce the risk of default. Our commercial mortgage loans on real estate are reported at cost, net of loan loss allowances and deferred prepayment fees. At December 31, 2017 and 2016, the largest principal amount outstanding for any single mortgage loan was $21.2 million and $20.9 million, respectively, and the average loan size was $3.5 million and $3.2 million, respectively. In addition, the average loan to value ratio for the overall portfolio was 53.6% and 53.7%, at December 31, 2017 and 2016, respectively, based upon the underwriting and appraisal at the time the loan was made. This loan to value is indicative of our conservative underwriting policies and practices for making commercial mortgage loans and may not be indicative of collateral values at the current reporting date. Our current practice is to only obtain market value appraisals of the underlying collateral at the inception of the loan unless we identify indicators of impairment in our ongoing analysis of the portfolio, in which case, we either calculate a value of the collateral using a capitalization method or obtain a third party appraisal of the underlying collateral. The commercial mortgage loan portfolio is summarized by geographic region and property type in Note 4 of our audited consolidated financial statements of this Form 10-K, which is incorporated by reference in this Item 7.
At December 31, 2017, we had no commercial mortgage loans that were delinquent (60 days or more past due at the reporting date) in their principal and interest payments.
Liquidity requirements are met primarily by funds provided from operations. Our life subsidiaries generally receive adequate cash flow from annuity deposits and investment income to meet their obligations. Annuity liabilities are generally long-term in nature. However, a primary liquidity concern is the risk of an extraordinary level of early policyholder withdrawals. We include provisions within our annuity policies, such as surrender charges and bonus vesting, which help limit and discourage early withdrawals. Our lifetime income benefit rider also limits the risk of early withdrawals as it provides an additional liquidity option to policyholders as the policyholder can elect to receive guaranteed payments for life from their contract without requiring them to annuitize their contract value and the rider is not transferable to other contracts. At December 31, 2017, approximately 94% of our annuity liabilities were subject to penalty upon surrender, with a weighted average remaining surrender charge period of 8.1 years and a weighted average surrender charge percentage of 13.0%.
Our insurance subsidiaries continue to have adequate cash flows from annuity deposits and investment income to meet their policyholder and other obligations. Net cash flows from annuity deposits and funds returned to policyholders as surrenders, withdrawals and death claims were $1.3 billion for the year ended December 31, 2017 compared to $3.2 billion for the year ended December 31, 2016 with the decrease attributable to a $1.6 billion decrease in net annuity deposits after coinsurance and a $311.6 million (after coinsurance) increase in funds returned to policyholders. We continue to invest the net proceeds from policyholder transactions and investment activities in high quality fixed maturity securities and fixed rate commercial mortgage loans.
We, as the parent company, are a legal entity separate and distinct from our subsidiaries, and have no business operations. We need liquidity primarily to service our debt (senior notes and subordinated debentures issued to subsidiary trusts), pay operating expenses and pay dividends to stockholders. Our assets consist primarily of the capital stock and surplus notes of our subsidiaries. Accordingly, our future cash flows depend upon the availability of dividends, surplus note interest payments and other statutorily permissible payments from our subsidiaries, such as payments under our investment advisory agreements and tax allocation agreement with our subsidiaries. Payments under our investment advisory agreements and tax allocation agreement with our subsidiaries provide adequate cash flow for us to meet our current and reasonably foreseeable future obligations and we expect they will be adequate to fund our parent company cash flow requirements in 2018.
The transfer of funds by American Equity Life is also restricted by a covenant in our line of credit agreement which requires American Equity Life to maintain a minimum risk-based capital ratio of 275% and a minimum level of statutory surplus equal to the sum of 1) 80% of statutory surplus at June 30, 2016, 2) 50% of the statutory net income for each fiscal quarter ending after June 30, 2016, and 3) 50% of all capital contributed to American Equity Life after June 30, 2016. American Equity Life's risk-based capital ratio was 378% at December 31, 2017. Under this agreement, we are also required to maintain a maximum ratio of adjusted debt to total adjusted capital of 0.35.
Cash and cash equivalents of the parent holding company at December 31, 2017, were $21.0 million. In addition, as discussed in Note 9 to our audited consolidated financial statements we have a $150 million revolving line of credit agreement, with no borrowings outstanding at December 31, 2017. This revolving line of credit terminates on September 30, 2021, and borrowings are available for general corporate purposes of the parent company and its subsidiaries. We also have the ability to issue equity, debt or other types of securities through one or more methods of distribution under a currently effective shelf registration statement on Form S-3. The terms of any offering would be established at the time of the offering, subject to market conditions.
As discussed above under Executive Summary, we issued the 2027 Notes on June 16, 2017. We used the net proceeds from the issuance of the 2027 Notes to prepay our $100 million term loan that was scheduled to mature in 2019 on June 16, 2017, and to redeem the 2021 Notes on July 17, 2017. We paid $413.3 million to redeem the 2021 Notes which included an early redemption premium equal to 3.313% of the $400 million principal amount of the 2021 Notes.
We utilize the models from a leading structured product software specialist serving institutional investors. These models incorporate each security's seniority and cash flow structure. In circumstances where the analysis implies a potential for principal loss at some point in the future, we use our "best estimate" cash flow projection discounted at the security's effective yield at acquisition to determine the amount of our potential credit loss associated with this security. The discounted expected future cash flows equates to our expected recovery value. Any shortfall of the expected recovery when compared to the amortized cost of the security will be recorded as the credit loss component of an other than temporary impairment.
In addition, for debt securities which we do not intend to sell and it is not more likely than not we will be required to sell, but our intent changes due to changes or events that could not have been reasonably anticipated, an other than temporary impairment charge is recognized in net income and amortized cost is written down to fair value. Once an impairment charge has been recorded, we then continue to review the other than temporarily impaired securities for appropriate valuation on an ongoing basis. Unrealized losses may be recognized in future periods through a charge to earnings should we later conclude that the decline in fair value below amortized cost is other than temporary pursuant to our accounting policy described above. The use of different methodologies and assumptions to determine the fair value of investments and the timing and amount of impairments may have a material effect on the amounts presented in our consolidated financial statements.
The most sensitive assumption in determining policy liabilities for fixed index annuities is the rates used to discount the excess projected contract values. As indicated above, the discount rate reflects our nonperformance risk. If the discount rates used to discount the excess projected contract values at December 31, 2017 were to increase by 100 basis points, our reserves for fixed index annuities would decrease by $579.5 million recorded through operations as a decrease in the change in fair value of embedded derivatives and there would be a corresponding decrease of $339.4 million to our combined balance for deferred policy acquisition costs and deferred sales inducements recorded through operations as an increase in amortization of deferred policy acquisition costs and deferred sales inducements. A decrease by 100 basis points in the discount rate used to discount the excess projected contract values would increase our reserves for fixed index annuities by $645.8 million recorded through operations as an increase in the change in fair value of embedded derivatives and increase our combined balance for deferred policy acquisition costs and deferred sales inducements by $374.8 million recorded through operations as a decrease in amortization of deferred policy acquisition costs and deferred sales inducements.
Estimated future gross profits vary based on a number of sources including investment spread margins, lifetime income benefit rider fees and benefits, surrender charge income, policy persistency, policy administrative expenses and realized gains and losses on investments including credit related other than temporary impairment losses. Estimated future gross profits are most sensitive to changes in investment spread margins which are the most significant component of gross profits. If estimated gross profits for all future years on business in force at December 31, 2017 were to increase by 10%, our combined balance for deferred policy acquisition costs and deferred sales inducements at December 31, 2017 would increase by $194.1 million recorded through operations as a decrease to amortization of deferred policy acquisition costs and deferred sales inducements. Correspondingly, a 10% decrease in estimated gross profits for all future years would result in a $215.1 million decrease in the combined December 31, 2017 balances recorded through operations as an increase to amortization of deferred policy acquisition costs and deferred sales inducements.