During calendar year 2026
During 2026 but by 10/15/2026 – For tax year 2025 - Last day to file Form 1040 that’s on an automatic extension
By 4/15/2026 – For tax year 2025 - Forms 1040 and 4868 - automatic extension of time to file but not time to pay for form 1040 – tax year 2025
Estimated tax payments - all for tax year 2027
4/18/2026 – 1st quarter
6/15/2026 – 2nd quarter
9/15/2026 – 3rd quarter
1/16/2027 – 4th quarter