institutions . international paper continually monitors its positions with and the credit quality of these financial institutions and does not expect non- performance by the counterparties . note 14 capital stock the authorized capital stock at both december 31 , 2006 and 2005 , consisted of 990850000 shares of common stock , $ 1 par value ; 400000 shares of cumulative $ 4 preferred stock , without par value ( stated value $ 100 per share ) ; and 8750000 shares of serial preferred stock , $ 1 par value . the serial preferred stock is issuable in one or more series by the board of directors without further shareholder action . in july 2006 , in connection with the planned use of projected proceeds from the company 2019s trans- formation plan , international paper 2019s board of direc- tors authorized a share repurchase program to acquire up to $ 3.0 billion of the company 2019s stock . in a modified 201cdutch auction 201d tender offer completed in september 2006 , international paper purchased 38465260 shares of its common stock at a price of $ 36.00 per share , plus costs to acquire the shares , for a total cost of approximately $ 1.4 billion . in addition , in december 2006 , the company purchased an addi- tional 1220558 shares of its common stock in the open market at an average price of $ 33.84 per share , plus costs to acquire the shares , for a total cost of approximately $ 41 million . following the completion of these share repurchases , international paper had approximately 454 million shares of common stock issued and outstanding . note 15 retirement plans u.s . defined benefit plans international paper maintains pension plans that provide retirement benefits to substantially all domestic employees hired prior to july 1 , 2004 . these employees generally are eligible to participate in the plans upon completion of one year of service and attainment of age 21 . employees hired after june 30 , 2004 , who are not eligible for these pension plans receive an additional company contribution to their savings plan ( see 201cother plans 201d on page 83 ) . the plans provide defined benefits based on years of credited service and either final average earnings ( salaried employees ) , hourly job rates or specified benefit rates ( hourly and union employees ) . for its qualified defined benefit pension plan , interna- tional paper makes contributions that are sufficient to fully fund its actuarially determined costs , gen- erally equal to the minimum amounts required by the employee retirement income security act ( erisa ) . in addition , international paper made volun- tary contributions of $ 1.0 billion to the qualified defined benefit plan in 2006 , and does not expect to make any contributions in 2007 . the company also has two unfunded nonqualified defined benefit pension plans : a pension restoration plan available to employees hired prior to july 1 , 2004 that provides retirement benefits based on eligible compensation in excess of limits set by the internal revenue service , and a supplemental retirement plan for senior managers ( serp ) , which is an alternative retirement plan for senior vice presi- dents and above who are designated by the chief executive officer as participants . these nonqualified plans are only funded to the extent of benefits paid , which are expected to be $ 41 million in 2007 . net periodic pension expense service cost is the actuarial present value of benefits attributed by the plans 2019 benefit formula to services rendered by employees during the year . interest cost represents the increase in the projected benefit obli- gation , which is a discounted amount , due to the passage of time . the expected return on plan assets reflects the computed amount of current year earn- ings from the investment of plan assets using an estimated long-term rate of return . net periodic pension expense for qualified and nonqualified u.s . defined benefit plans comprised the following : in millions 2006 2005 2004 .

Table: in millions 2006 2005 2004 service cost $ 141 $ 129 $ 115 interest cost 506 474 467 expected return on plan assets -540 ( 540 ) -556 ( 556 ) -592 ( 592 ) actuarial loss 243 167 94 amortization of prior service cost 27 29 27 net periodic pension expense ( a ) $ 377 $ 243 $ 111

( a ) excludes $ 9.1 million , $ 6.5 million and $ 3.4 million in 2006 , 2005 and 2004 , respectively , in curtailment losses , and $ 8.7 million , $ 3.6 million and $ 1.4 million in 2006 , 2005 and 2004 , respectively , of termination benefits , in connection with cost reduction programs and facility rationalizations that were recorded in restructuring and other charges in the con- solidated statement of operations . also excludes $ 77.2 million and $ 14.3 million in 2006 and 2005 , respectively , in curtailment losses , and $ 18.6 million and $ 7.6 million of termination bene- fits in 2006 and 2005 , respectively , related to certain divest- itures recorded in net losses on sales and impairments of businesses held for sale in the consolidated statement of oper- ations. .

Question: what is the percentage change in net periodic pension expense between 2005 and 2006?
Answer: 55%
Calculation: divide(subtract(377, 243), 243)