Q4 Estimated Tax Payment: Due January 15, 2027

The "quarters" are not equal. Q4 spans four months of income, which is why it is the installment where late-year bonuses, RSU vests, property sales and year-end distributions show up. It is also the last chance to finish 2026 before the penalty math locks.

For the whole-year rules (who must pay, the three payment targets, and how the safe harbor works), start with the estimated tax payments guide. For every other 2026 and early 2027 date, see the full tax deadline calendar.

The penalty test is cumulative. By each due date, your payments should add up to 25%, 50%, 75% and then 100% of your required annual payment. So the Q4 number is whatever closes the gap to 100%:

1. Find your required annual payment. The smaller of 90% of projected 2026 tax or 100% of 2025 total tax. Use 110% of 2025 tax if 2025 AGI was over $150,000 ($75,000 married filing separately). The prior-year option requires that 2025 was a full 12-month tax year.
2. Subtract the 2026 estimates you have actually paid, including any 2025 overpayment you applied to 2026.
3. Subtract your full-year 2026 withholding: W-2 wages, S-corp salary, bonuses, pension and IRA withholding, and backup withholding.
4. Pay the remainder by January 15, 2027. If the result is negative, you are already inside the harbor.

A rising-income year almost always points to the prior-year number because it is fixed. A down year can point to 90% of the current-year tax, but that requires a real projection through December 31. Our estimated tax penalty calculator runs both tests and shows any quarter that falls short.

This is the single most useful fact about the last weeks of the year. An estimated payment counts on the day you make it. Withholding counts as if one quarter of it was paid on each of the four due dates, no matter when it actually came out of a paycheck.

That asymmetry is why the withholding row in the example above shows no penalty. The $44,000 withheld in December is treated as $11,000 paid on April 15, $11,000 on June 15, $11,000 on September 15 and $11,000 on January 15. The early quarters become overpaid, the overpayments roll forward, and the September hole is filled retroactively.

Ways to create withholding before December 31, 2026:

• A new Form W-4 with a flat extra amount per pay period (line 4(c)) for the last December paychecks, yours or your spouse's on a joint return.
• S-corp owners: a year-end salary payment run through payroll with heavy federal withholding. Keep the salary within reasonable compensation rules.
• Retirees and IRA owners: a distribution with federal withholding elected. The distribution itself is usually taxable income, so count it in the math before you size the withholding.

Publication 505 gives one exception: file your complete 2026 Form 1040 and pay everything you owe by January 31, 2027, and the January 15 installment carries no penalty. January 31, 2027 falls on a Sunday, so we treat Friday, January 29, 2027 as the working deadline.

Two limits make this less useful than it sounds:

• It only covers Q4. Any shortfall from April, June or September still carries its penalty.
• Most people cannot file that fast. Brokerage 1099-B forms often arrive in mid-February and partnership K-1s much later. If your return depends on either, plan on making the January 15 payment.

If your income landed late in the year, read how the annualized income installment method lets the Q4 payment carry most of the year, and how it applies to estimated tax on capital gains.

Most states with an income tax also set a final 2026 installment in mid-January 2027, but the percentages and safe harbors are state law, not the federal rule. California, for example, uses a 30/40/0/30 schedule, so its January installment is 30% of the year; see the California estimated tax guide.

The timing choice matters if you itemize. A state estimated payment made by December 31, 2026 generally counts toward your 2026 state and local tax deduction, subject to the SALT cap. The same payment made in January belongs to 2027. If you are already at the cap or take the standard deduction, January costs you nothing and keeps the cash longer.

The penalty is interest-like, not a flat fine. A missed Q4 installment accrues from January 15 until you pay it, capped at April 15, 2027, the return due date. At 7%, a $22,000 shortfall that waits the full 90 days costs about $380. The rate for January 2027 onward will be announced by the IRS later this year, so treat that as an estimate.

Pay as soon as you notice, using IRS Direct Pay or EFTPS, and choose tax year 2026 when you do. The IRS usually computes the penalty and bills you; see the Form 2210 penalty guide for when you file the form yourself and when a waiver applies.