The September 15 Tax Deadline Retirees Miss — and the December Fix the IRS Actually Allows
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The September 15 Tax Deadline Retirees Miss — and the December Fix the IRS Actually Allows

Third-quarter estimated taxes are due September 15, and the IRS underpayment rate stays at 7% through year-end. But withholding and estimated payments are not credited the same way, and that asymmetry gives retirees a fix that runs all the way to December 31.

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A Deadline Without an Employer Behind It

The third 2026 estimated tax installment is due September 15. For working savers this passes unnoticed — payroll withholds every two weeks. Retirees lose that machinery. IRA distributions, pension income, dividends, capital gains and taxable Social Security arrive largely untaxed unless the retiree affirmatively arranges otherwise, and the four installment dates are April 15, June 15, September 15 and January 15, 2027.

Miss enough of them and the IRS charges an underpayment penalty that is really interest. On August 21, 2026, the IRS announced rates for the fourth quarter would hold at 7% for noncorporate underpayments, compounded daily — the federal short-term rate plus three percentage points. That is the same 7% that applied in the third quarter.

The Three Safe Harbors

You avoid the penalty entirely if any one of these holds:

  • You owe less than $1,000 after subtracting withholding and refundable credits.
  • You pay 90% of your 2026 tax.
  • You pay 100% of the tax shown on your 2025 return — but 110% if your 2025 adjusted gross income exceeded $150,000 ($75,000 if married filing separately).

The prior-year harbor is the useful one, because it is a known number. You can read it off last year's return today. A Roth conversion or a large capital gain can double your current-year tax and still leave you penalty-free, provided you covered 100% or 110% of last year's figure.

The Asymmetry Almost Nobody Uses

Here is the mechanism that matters. Estimated tax payments are credited on the date you actually pay them. Withholding is not. The IRS instructions for Form 2210 state it plainly:

"For withheld federal income tax and excess social security or tier 1 RRTA, you are considered to have paid one-fourth of these amounts on each payment due date unless you can show otherwise."

A dollar withheld on December 28 is therefore treated as though one quarter of it was paid back on April 15. A dollar sent as an estimated payment on December 28 is treated as four months late. Same dollar, same day, different result.

That is why a retiree who reaches October realizing they have underpaid all year is not out of options. The lever is withholding:

  • Form W-4R governs nonperiodic IRA distributions. The default is 10%, but you may elect any rate from 0% to 100%.
  • Form W-4P sets withholding on periodic pension and annuity payments.
  • Form W-4V allows voluntary Social Security withholding, but only at 7%, 10%, 12% or 22% — no custom percentages, no flat dollar amounts.

A year-end distribution with a large withholding election can retroactively plug all four quarters at once.

The Caveats That Keep This Honest

The distribution itself is taxable income, so withholding 100% of a $20,000 withdrawal does not cover $20,000 of other tax — it covers that amount minus the tax the withdrawal creates. Under age 59½, the distribution may also trigger the 10% early-withdrawal penalty, and withheld dollars cannot be rolled over. The one-fourth rule is a default, not a mandate: if actual withholding dates help you more, you may elect them by checking box D and attaching Form 2210. And retirees with genuinely lumpy income — a single large gain in Q4 — often do better with the annualized installment method on Form 2210's Schedule AI, which matches required payments to when income was actually received.

Practical Takeaways

  1. Pull your 2025 return and find your total tax. That number, times 100% or 110%, is your target.
  2. If you are short, make the September 15 payment anyway — the penalty accrues per installment, so paying now stops future accrual even though it does not undo interest already run.
  3. Then set withholding on a year-end IRA distribution or pension payment to close the remaining gap before December 31.
  4. If your income was concentrated late in the year, run Schedule AI before assuming you owe a penalty at all.

Sources: IRS Instructions for Form 2210; IRS Tax Topic 306 – Penalty for Underpayment of Estimated Tax; IRS Newsroom, "Interest rates remain the same for the fourth quarter of 2026" (August 21, 2026); IRS Form W-4R (2026); IRS Form W-4V (Rev. January 2026); IRS Publication 505, Tax Withholding and Estimated Tax.

This article is educational and not tax advice. Consult a qualified tax professional about your situation.

estimated taxesretirement planningIRAtax planningwithholdingForm 2210