Retirees who opted out of federal income tax withholding on their pension or annuity checks have a hard deadline approaching: September 15 is the due date for third-quarter estimated tax payments covering income earned from June 1 through August 31. Missing that date, or sending less than the required amount, triggers an IRS-assessed penalty that compounds for each day the payment is late.
Why the September 15 deadline hits retirees harder than wage earners
Wage earners rarely think about estimated taxes because their employers withhold federal income tax from every paycheck. Retirees, by contrast, can file a Form W-4P to reduce or eliminate withholding on distributions from pensions, annuities, and certain deferred-income accounts. Federal law under Section 3405 allows that election, but it shifts the burden of timely payment entirely onto the retiree. Those who skip withholding must instead send quarterly installments to the IRS or risk an addition-to-tax penalty.
The quarterly schedule divides the tax year into four income periods, each with its own due date. The third installment, covering June 1 through August 31, falls on September 15. The Taxpayer Advocate Service flags this date on its annual tax calendar as one of the most commonly missed deadlines for people living on retirement income. Because Social Security cost-of-living adjustments can raise total taxable income in ways retirees do not anticipate mid-year, the gap between what they owe and what they have paid can widen by the third quarter, making the September 15 installment especially consequential.
How IRS penalties apply under Section 6654 and Form 2210
The penalty for underpaying estimated tax is not discretionary. It is written into Section 6654, which creates an automatic addition to tax when an individual fails to pay enough by each installment deadline. The IRS does not need to send a warning letter first. The charge accrues from the missed due date until the tax is paid or until the filing deadline for the return, whichever comes first.
Retirees who discover the shortfall at tax time typically encounter Form 2210, which is used to compute the underpayment penalty for individuals, estates, and trusts. The form walks filers through each quarterly period, compares required installments against actual payments and withholding credits, and calculates the penalty owed. The IRS also posts a detailed explanation of the underpayment penalty, including how it is figured and when it applies, on its website. The calculation functions like interest: the IRS applies a rate, set quarterly, to the amount that should have been paid for each period but was not.
Unlike some other penalties, this one can apply even if a retiree ultimately pays the full tax bill by April 15. What matters is whether enough tax was paid during the year, in roughly even installments, to satisfy the rules in Section 6654. Large “catch-up” payments late in the year may reduce the final balance due but still leave earlier quarters underpaid, which is why the September 15 deadline is so important.
Safe harbors and planning options for retirees
IRS guidance in Publication 505 explains how retirees can avoid underpayment altogether by using safe-harbor rules. In general, individuals escape the penalty if they pay in at least 90 percent of the current year’s tax, or 100 percent of the prior year’s tax, through a combination of withholding and estimated payments. For higher-income taxpayers, the prior-year percentage may be higher, but the principle is the same: meet the safe harbor and the penalty does not apply, even if the final return shows a balance due.
For retirees, the most flexible tool is often withholding on retirement distributions. Unlike estimated payments, which must be made by fixed quarterly dates, withholding on pensions and annuities is treated as if it were paid evenly throughout the year, no matter when it is actually taken out. That means a retiree who realizes in late summer that earlier installments were too low can sometimes increase withholding on fall distributions to help close the gap for all four quarters.
Another option is to adjust the pattern of estimated payments themselves. Retirees whose income is uneven-such as those taking larger distributions late in the year-can use the “annualized income installment method” on Form 2210 to match required payments more closely to when income is actually received. This can reduce or eliminate penalties for earlier quarters if most of the income arrived later.
What to do before September 15
Retirees who have not yet evaluated their 2026 tax position should compare year-to-date income, withholding, and estimated payments against last year’s total tax. If payments are tracking below the safe-harbor thresholds described in Publication 505, sending an additional estimated payment by September 15 can limit the exposure for the third quarter and reduce the chance of a surprise penalty at filing time.
Those relying primarily on pension or annuity income may also want to revisit their Form W-4P elections. Increasing withholding for the remainder of the year can provide a backstop if future estimated payments are missed or miscalculated. While no single strategy fits every retiree, acting before the September deadline is far more effective than trying to fix an underpayment after the year has closed and the penalty has already begun to accrue.
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