The deadline to amend your 2020 and/or 2021 tax return for claiming or adjusting SETC credits is three years from the original due date of the return or within two years from the date you paid the tax, whichever is later. The deadline for filing for the SETC tax credits for your 2020 tax return is April 15, 2024, and your 2021 tax return is April 15, 2025, unless you filed an extension