Safe harbor
You avoid the underpayment penalty if withholding plus timely estimated payments cover the smaller of 90% of this year’s tax or 100% of last year’s (110% if last year’s AGI was over $150,000), or you owe less than $1,000.
FAQ
When are 2026 estimated taxes due?
April 15, June 15 and September 15, 2026, and January 15, 2027.
Sources (checked Nov 6, 2026): IRS Form 1040-ES (2026); IRC sec. 6654.