Cash, Cash Equivalents and Marketable Securities
Cash, cash equivalents, and marketable securities increased by $485.5 million to $2,455.2 million as at December 31, 2019 from $ 1,969.7 million as at December 31, 2018, primarily as a result of proceeds from the public offering in September 2019, cash provided by our operating activities, and proceeds from the exercise of stock options.
Cash equivalents and marketable securities include money market funds, repurchase agreements, term deposits, U.S. and Canadian federal bonds, corporate bonds, and commercial paper, all maturing within the 12 months from December 31, 2019.
The following table summarizes our total cash, cash equivalents and marketable securities as at December 31, 2019 and 2018 as well as our operating, investing and financing activities for the years ended December 31, 2019 and 2018:
Cash Flows From Operating Activities
Our largest source of operating cash is from subscription solutions. These payments are typically paid to us at the beginning of the applicable subscription period, except for our Shopify Plus merchants who typically pay us at the end of their monthly billing cycle. We also generate significant cash flows from our Shopify Payments processing fee arrangements, which are received on a daily basis as transactions are processed. Our primary uses of cash from operating activities are for third-party payment processing fees, employee-related expenditures, advancing funds to merchants through Shopify Capital, marketing programs, third-party shipping and fulfillment partners, outsourced hosting costs, and leased facilities.
For the year ended December 31, 2019, cash provided by operating activities was $70.6 million. This was primarily as a result of our net loss of $124.8 million, which once adjusted for $158.5 million of stock-based compensation expense, $35.7 million of amortization and depreciation, a $37.9 million increase in deferred income taxes, a $15.9 million increase of our provision for uncollectible merchant cash advances and loans, and an unrealized foreign exchange loss of $3.2 million, contributed $50.4 million of positive cash flows. Additional cash of $162.9 million resulted from the following increases in operating liabilities: $84.6 million in accounts payable and accrued liabilities due to indirect taxes payable, payroll liabilities, and payment processing and interchange fees; $64.6 million in income tax assets and liabilities; $12.3 million in deferred revenue due to the growth in sales of our subscription solutions along with the acquisition of 6RS; and $1.5 million increase in net lease liabilities. These were offset by $142.8 million of cash used resulting from the following increases in operating assets: $74.2 million in merchant cash advances and loans as we continued to grow Shopify Capital; $56.2 million in trade and other receivables; and $12.4 million in other current assets driven primarily by an increase in prepaid expenses, forward contract assets designated for hedge accounting, and deposits.
For the year ended December 31, 2018, cash provided by operating activities was $9.3 million. This was primarily as a result of our net loss of $64.6 million, which once adjusted for $95.7 million of stock-based compensation expense, $27.1 million of amortization and depreciation, a $5.9 million increase of our provision for uncollectible merchant cash advances, and an unrealized foreign exchange loss of $1.3 million, contributed $65.4 million of positive cash flows. Additional cash of $38.1 million resulted from the following increases in operating liabilities: $20.6 million in accounts payable and accrued liabilities; $9.0 million in deferred revenue; and $8.4 million in lease liabilities. These were offset by $94.2 million of cash used resulting from the following increases in operating assets: $50.7 million in merchant cash advances and loans; $32.6 million in trade and other receivables; and $10.8 million in other current assets.
Cash Flows From Investing Activities
Cash flows used in investing activities are primarily related to the purchase and sale of marketable securities, business acquisitions, purchases of leasehold improvements and furniture and fixtures to support our expanding infrastructure and workforce, purchases of computer equipment, and software development costs eligible for capitalization.
Net cash used in investing activities in the year ended December 31, 2019 was $ 569.5 million, which was driven by $265.5 million used to make business acquisitions, most of which was for the 6RS acquisition on October 17, 2019, net purchases of $241.6 million in marketable securities, $ 56.8 million used to purchase property and equipment, which primarily consisted of expenditures on leasehold improvements, and $5.6 million used for purchasing and developing software to add functionality to our platform and support our expanding merchant base.
Net cash used in investing activities in the year ended December 31, 2018 was $810.6 million, reflecting net purchases of $749.7 million in marketable securities. Cash used in investing activities also included $28.0 million used to purchase property and equipment, which primarily consisted of expenditures on leasehold improvements, $19.4 million used to make business acquisitions, and $13.6 million used for purchasing and developing software.
Cash Flows From Financing Activities
To date, cash flows from financing activities have related to proceeds from private placements, public offerings, and exercises of stock options.
Net cash provided by financing activities in the year ended December 31, 2019 was $736.4 million driven mainly by the $688.0 million raised by our September 2019 public offering, and $48.3 million in proceeds from the issuance of Class A subordinate voting shares and Class B multiple voting shares as a result of stock option exercises. This compares to $1,072.2 million for the same period in 2018 of which $1,041.7 million was raised by our February and December 2018 public offerings while the remaining $30.5 million related to stock option exercises.
Table:
 | Years ended December 31, | 
 | 2019 | 2018
 | (in thousands) | 
Cash, cash equivalents and marketable securities (end of period) | $2,455,194 | 1,969,670
Net cash provided by (used in): |  | 
Operating activities | $70,615 | $9,324
Investing activities | (569,475) | (810,633)
Financing activities | 736,351 | 1,072,182
Effect of foreign exchange on cash and cash equivalents | 1,742 | (1,867)
Net increase in cash and cash equivalents | 239,233 | 269,006
Change in marketable securities | 246,291 | 762,625
Net increase in cash, cash equivalents and marketable securities | $485,524 | $1,031,631


Question: What is Shopify's largest source of operating cash from?
Answer: subscription solutions