You avoid the underpayment penalty if withholding plus timely estimates are at least the smaller of:
90% of this year's total tax, or
100% of last year's total tax (110% if last year's AGI was over $150,000; $75,000 if married filing separately).
You also don't owe a penalty if:
you'll owe less than $1,000 after withholding and credits, or
you had zero tax liability last year for a full 12-month year.
2026 due dates
Apr 15, 2026
Jun 15, 2026
Sep 15, 2026
Jan 15, 2027
You can skip the Jan 15 payment if you file your 2026 return by Jan 31, 2027 and pay in full. 2027 dates aren't listed here yet.
Easiest fix for a W-2 + 1099 nurse
Raise W-2 withholding (Form W-4 line 4c). Withholding is treated as paid evenly through the year, so increasing it late in the year still covers earlier quarters (Pub 505).
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Who must pay: generally anyone expecting to owe $1,000 or more at filing after withholding and credits.
For the penalty calculation, withholding is treated as paid one-fourth on each due date, so extra withholding late in the year still covers earlier quarters. (Pub 505 (2026))
Have 1099 side income? Here's how to avoid the underpayment penalty.
2026 due dates: April 15, June 15, September 15, 2026, and January 15, 2027.
Safe harbor: 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). Generally no penalty if you'll owe less than $1,000 after withholding. (Pub 505 (2026))
The easiest fix for W-2 plus 1099: raise W-2 withholding. It counts as paid evenly through the year.
Research, not tax advice. Confirm with a CPA or EA before filing.