Kodiak Sciences Inc. Notes to Consolidated Financial Statements (in thousands, except share and per share data) 101 As of December 31, 2023, the Company had $83.8 million of federal and $616.3 million of state net operating loss availabl a e to offs f et future taxabl a e income. A portion of the federal net operating loss carryforwards begin to expire in 2035 and the state net operating loss carryforwards begin to expire in 2035, if not utilized. $65.6 million of the federal net operating loss are not subj u ect to expiration. As of December 31, 2023, the Company also had federal and state research and development credit carryforwards of approximately $28.9 million and $9.0 million, respectively. The federal research and development credit carryforwards expire beginning 2035. The California tax credit can be carried forward indefinitely. Califor f nia Senate Bill 113 (SB 113), was signed into law by Governor Newsom on Februa r ry 9, 2022. The legislation contains important California tax law changes, including reinstatement of business tax credits and net NOL deductions limited by AB 85 mentioned above. Given the Company’s taxabl a e loss position, this legislation did not impact the tax provision for the years ended December 31, 2023 or 2022. A reconciliation of the Company’s effe f ctive tax rate to the statut t ory r U.S. federal rate is as follows: December 31, 2023 December 31, 2022 December 31, 2021 Federal statut t ory r income tax rate 21.0% 21.0% 21.0% State taxes (2.6) 5.8 6.7 Foreign tax rate differential (4.3) (4.7) (7.7) Change in valuation allowance (10.5) (20.0) (78.3) Stock-based compensation (4.1) (3.9) (1.2) Research tax credit 1.4 1.8 2.4 Other (0.1) — — Sale of future royalties — — 0.1 Section 162(m) — — (0.8) Intangible valuation (0.8) — 57.8 Provision for income taxes 0.0% 0.0% 0.0% The Company recognizes benefits of uncertain tax positions if it is more likely than not that such positions will be sustained upon examination based solely on their technical merits, as the largest amount of benefit that is more likely than not to be realized upon the ultimate settlement. As of December 31, 2023, 2022 and 2021, none of the unrecognized tax benefits would affe f ct income tax expense with consideration of the valuation allowance. The Company does not anticipate the uncertain tax positions will materially change in the next 12 months. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense or benefit. To date, there have been no interest or penalties charged in relation to the unrecognized tax benefits. The beginning and ending unrecognized tax benefits amounts are as follows (in thousands): December 31, 2023 December 31, 2022 December 31, 2021 Unrecognized tax benefits at beginning of period $ 7,578 $ 6,729 $ 4,650 Increases related to current year tax positions 667 849 2,079 Unrecognized tax benefits at end of period $ 8,245 $ 7,578 $ 6,729 The Company files income tax returns in the United States and Switzerland. The Swiss Federal Tax Administration is currently conducting examinations of the Company's tax returns for the years 2018 through 2022. All US tax returns remain open for examination by the federal and state authorities for three and four years, respectively, from the date of utilization of any net operating loss or credits.