Missed the Sept. 15 IRS Tax Deadline? Retirees Who Took Big IRA Withdrawals Have a Fix Before Dec. 31

The Sept. 15, 2026 deadline for third-quarter estimated taxes has come and gone. For retirees who took a five-figure withdrawal from a traditional IRA this summer and let the default 10% withholding rate cover it, the tax bill is now exposed and the penalty clock is running.

The IRS calls it an underpayment penalty. It functions like interest, calculated quarterly against the federal short-term rate plus three percentage points. In IR-2026-98, released Aug. 21, the IRS confirmed the rate for individuals stays at 7% annualized through Dec. 31, after dipping to 6% during the second quarter.

Why the Default Withholding Falls Short

Custodians withhold 10% by default on a one-time IRA distribution and 20% on a one-time 401(k) distribution, according to IRS Form W-4R. Neither comes close to covering the actual tax on a large withdrawal for most retirees, especially once Social Security becomes partly taxable. The Social Security Administration says benefits become taxable once combined income passes $25,000 for single filers or $32,000 for married couples filing jointly, and nothing gets withheld from those benefits automatically.

A CPA writing for Money Talks News, licensed since 1981, laid out the arithmetic before the deadline hit: a retiree who owes $6,000 for the year with zero withholding has a $1,500 installment due each quarter. Skip the September payment and let it ride to April 15 instead, and that $1,500 sits unpaid for seven months at 7% annualized, roughly $61. Skip all four installments and the total penalty for the year runs close to $250.

The Fix Hides in How the IRS Credits Withholding

Section 6654(g)(1) of the Internal Revenue Code treats two nearly identical dollars completely differently. Estimated tax payments are credited only on the exact date the IRS receives them, and each payment satisfies only the installment period in which it lands, according to IRS Publication 505. A payment mailed in December cannot retroactively erase a penalty that already started accruing in April.

Federal withholding works under a separate rule. Tax withheld from pensions, Social Security, and retirement account distributions is treated as paid evenly across all four installment periods of the year, regardless of when the money was actually collected, Publication 505 confirms.

That asymmetry creates the opening. A retiree who arranges a new distribution from a traditional IRA, 401(k), or pension before Dec. 31 and directs a large share of it to federal withholding can have that withholding applied evenly across the first three quarters retroactively, according to 24/7 Wall St. Done in one transaction, it can wipe out or sharply reduce penalties that already started building back in April and June.

A new distribution itself is taxable income, so the withholding has to be large enough to cover both the original shortfall and the tax generated by the fresh withdrawal. Some custodians allow up to 100% federal withholding on an IRA distribution; many require a signed election form, and the election has to be made when the distribution is processed. It cannot be applied after the fact to money already paid out.

This only works with traditional retirement accounts. Roth IRA distributions generate no taxable income and therefore no withholding, so they cannot be used to plug the gap, Publication 505 confirms. And while IRA withholding can be adjusted up or down, 401(k) withholding elected on a distribution can only be increased, not decreased, per Form W-4R rules.

The Safe Harbor Numbers That Matter

The penalty disappears entirely if withholding and timely estimated payments combined reach either 90% of the current year's total tax liability or 100% of the prior year's liability, whichever is smaller, according to Publication 505. Retirees whose prior-year adjusted gross income topped $150,000 (or $75,000 if married filing separately) have to hit 110% of last year's number instead. Because the prior-year figure is already fixed on last year's return, it's typically the easier target to aim for than guessing at an unfinished year's total.

The fourth-quarter estimated payment is due Jan. 15, 2027. Sending a check then stops the penalty from growing further but does nothing to erase what has already accrued for the earlier quarters, since ordinary estimated payments aren't credited retroactively the way withholding is.

A Separate Deadline for Plan Sponsors, Not Individuals

In a related but distinct development, the IRS issued guidance in its Sept. 17 bulletin clarifying that not all retirement-plan amendments tied to the SECURE Act and SECURE 2.0 Act have to be adopted by the previously stated year-end 2026 deadline, according to PLANADVISER. Required amendments are now tied to when they first appear on the IRS's annual Required Amendment List, with some Roth catch-up provisions not due until Dec. 31, 2029. That guidance applies to employers and plan administrators maintaining retirement plans, not to individual retirees managing their own distributions and withholding.

For retirees facing the Q1 through Q3 shortfall, the practical deadline is Dec. 31. Whether a given IRA custodian can process a new distribution with the necessary withholding election in time, and whether the retiree has enough account balance left to cover both the shortfall and the new tax bill, remains a case-by-case calculation best run before the last week of December.