The Q3 Tax Payment Is Due September 15 and the IRS Is Charging 7%. A Bigger Check Now Does Nothing for the April and June Quarters.

The IRS charges 7% and counts each quarter separately. Two moves can undo a year of missed payments — and most retirees have never heard of either.

The IRS is charging 7% a year on underpaid estimated tax for the quarter running July through September 2026 (IRS, “Quarterly interest rates,” page updated July 2, 2026). The third-quarter payment is due September 15 (IRS, Form 1040-ES). And if you skipped April and June and figured you’d square it up now with one larger payment — that isn’t how the math works.

The rule that surprises people

Income tax in this country is pay-as-you-go. If you’re retired, nobody is doing that for you automatically. Social Security, a pension, IRA withdrawals, CD interest, dividends — the tax on all of it is yours to send in during the year, either through withholding or four estimated payments (IRS, Topic no. 306, reviewed March 31, 2026).

Miss one and the IRS doesn’t average it out at the end. As the Form 2210 instructions put it, the penalty “is figured separately for each required payment.” A payment made September 15 is credited on September 15. It does nothing for a shortfall that started on April 15.

You’re clear of all this if you owe less than $1,000 after withholding and credits, or if your withholding plus estimated payments cover at least 90% of this year’s tax or 100% of last year’s — whichever is smaller. If your prior-year adjusted gross income topped $150,000 ($75,000 filing separately), that second number becomes 110% (IRS, Topic no. 306; Instructions for Form 2210).

What this means for your wallet

Say your required installment is $2,000 a quarter and you missed April and June. That’s $4,000 sitting underpaid. Carried at 7% to next April’s filing date, it runs somewhere around $250 — our arithmetic at the IRS’s current rate, and the IRS resets that rate every quarter, so it’s an estimate, not a bill.

Not ruinous. But it’s $250 for a paperwork problem, and there’s no reason to hand it over.

The December move that reaches backward

Here’s the piece worth writing down. Withholding and estimated payments are not treated the same way.

An estimated payment counts on the day you make it. Money withheld — from a pension, from Social Security, from an IRA distribution — gets spread out. The Form 2210 instructions say it plainly: you “are considered to have paid one-fourth of these amounts on each payment due date unless you can show otherwise.”

Read that again with a calendar in front of you. Tax withheld from an IRA withdrawal on December 10 is treated by the IRS as though one-fourth of it arrived on April 15, one-fourth on June 15, one-fourth on September 15, and one-fourth in January. A single distribution late in the year, with enough tax withheld from it, can cover installments you blew months ago.

If you’re 73 or older and taking a required minimum distribution anyway, this costs you nothing extra — you’re taking the money regardless (IRS, “Retirement plan and IRA required minimum distributions FAQs”). You can direct the custodian to withhold enough to cover your whole year’s tax, not just the tax on that one withdrawal. It isn’t a loophole somebody found on the internet: Kiplinger has written it up as the “RMD solution” for estimated taxes, and Michael Kitces has covered it for financial advisers in “Reducing Estimated Tax Penalties With IRA Distributions.”

Two things to watch

• December 31 is not the real deadline. Custodians can need one to three weeks to process a large distribution, which makes mid-December the date that matters (Kiplinger). Leaving it to the last week of the year is how people miss it entirely.
• Your state may not cooperate. Not every IRA custodian will withhold state income tax, and state rules vary. Ask before you assume the same move handles your state bill.

The waiver written for people like you

One more, and it’s genuinely senior-specific. The IRS can waive the underpayment penalty if you retired after reaching age 62 — or became disabled — during the tax year or the one before it, and the underpayment was due to reasonable cause rather than willful neglect (IRS, Topic no. 306; Instructions for Form 2210).

That is exactly the situation of someone whose income went from a paycheck with withholding to a mix of pensions and withdrawals, and who didn’t realize the quarterly clock had started. It isn’t automatic — you request it on Form 2210 and explain the circumstances. But it’s there, and it’s worth asking your preparer about by name if it fits.

The takeaway

If you’re current on your estimated taxes, make the September 15 payment and carry on. If you’re behind, don’t try to fix it with a bigger check this month — that money is credited the day it lands. Look instead at withholding from a December distribution, and, if you retired after 62 in 2025 or 2026, at the waiver.

Either way, the thing to do this week is small: find last year’s return, look at your total tax, and check whether what you’ve paid in so far is on pace for 100% of that number (or 110% if your prior-year AGI cleared $150,000). That one comparison tells you whether you have a problem at all.

This is information, not financial advice — talk to a licensed tax professional about your own situation. Rates, thresholds, and deadlines are current as of August 2026 and come from IRS publications; the IRS sets its interest rate quarterly, so verify at irs.gov before acting. Senior Savers is independent and is not affiliated with or endorsed by the IRS or any government agency. Want one plain-English money move each week, without the panic? Join the free Senior Savers newsletter — no pressure, we never call you, unsubscribe anytime.