Filing Late and Paying Late: The IRC 6651(c)(1) Overlap Math

Most people who are late filing are also late paying. That is not a coincidence. The return does not get filed because the money is not there. So the real-world question is not how either penalty works by itself. It is how the two work together.

The answer sits in one sentence of the Internal Revenue Code, and it produces three numbers worth memorizing: 5 percent, 22.5 percent, and 47.5 percent.

The two penalties, side by side

For the mechanics of each, see the failure-to-file guide and the failure-to-pay guide. This page is about the overlap.

The offset rule

IRC 6651(c)(1) says the failure-to-file addition is reduced by the failure-to-pay addition for any month (or fraction of a month) to which both apply. IRM 20.1.2.3.7.3 repeats it: for each month both penalties run, subtract the failure-to-pay amount from the failure-to-file amount.

In a month where nothing has been paid, that turns 5 percent plus 0.5 percent into 4.5 percent plus 0.5 percent. Total: 5 percent a month. Not 5.5.

Walking the months: where 22.5% and 47.5% come from

Take a return that is never filed and a balance that is never paid. Month by month:

After month five the failure-to-file penalty is capped. It stays at 22.5 percent net, because the 25 percent gross was reduced by the 2.5 percent of failure-to-pay that overlapped it. The failure-to-pay penalty keeps climbing at 0.5 percent until it reaches its own 25 percent cap in month 50. So the ceiling on the two combined is 22.5 plus 25, or 47.5 percent of the unpaid tax, before a dollar of interest.

That assumes the standard 0.5 percent rate the whole way. A notice of intent to levy raises the rate to 1 percent under IRC 6651(d), which gets to the same 47.5 percent ceiling much faster. See the 1 percent rate guide.

Worked example: three months late filing, two years late paying

Say your 2025 return shows $20,000 unpaid at the April 15, 2026 due date. You file in month three (between June 16 and July 15, 2026) with no payment. You pay the full $20,000 in month 24, before any levy notice.

That is 25.5 percent of the tax in penalties. Filing three months late cost $2,700. Paying two years late cost $2,400. The filing piece was the bigger number, and it took one-eighth of the time.

Worked example: the maximum

Same $20,000. Nothing filed and nothing paid for more than 50 months, at the standard rate the whole time.

When the offset does not apply

The offset only happens when both penalties run in the same month. Three common patterns where it does not matter:

• Filed late, paid on time. If all tax was paid by the due date, the failure-to-file base is zero under IRC 6651(b)(1). There is nothing to offset because there is no penalty.
• Filed on time, paid late. Only the failure-to-pay penalty runs. No failure-to-file penalty means no offset.
• Paid partway through. The offset for each month equals that month's actual failure-to-pay charge, which shrinks as payments reduce the unpaid tax. The failure-to-file penalty is still computed on the balance unpaid at the due date.

The minimum penalty overrides the offset

There is a floor. When an income tax return is more than 60 days late, the failure-to-file penalty cannot be less than the lesser of an inflation-adjusted dollar amount or 100 percent of the tax required to be shown. The last sentence of IRC 6651(c)(1) says the offset cannot reduce the failure-to-file penalty below that minimum. For returns required to be filed in 2026, the dollar figure is $525 (Rev. Proc. 2024-40).

Three months late on a $2,000 balance cost $555 in penalties, almost 28 percent. The minimum penalty guide shows where the floor stops mattering.

Checking your notice

1. Compute failure to pay month by month on the unpaid tax at the start of each month.
2. Compute failure to file gross: unpaid tax at the due date x 5% x months late, capped at 25%.
3. Subtract the failure-to-pay amounts for the months both penalties ran.
4. If the return was more than 60 days late, compare the result to the minimum and use the larger.
5. Add the two penalties.

IRM 20.1.2.3.8.7.1 walks through the same steps with a $5,000 example. If you want the background on why returns go unfiled and what follows, see Unfiled Tax Returns: What Happens.

Worked example: a payment in the middle

Partial payments change the offset, so they deserve their own example. Say $10,000 was unpaid at the April 15, 2026 due date. You send $4,000 on May 20, 2026, which falls in penalty month two. You file the return and pay the remaining $6,000 in month four, in early August.

Failure to pay is computed month by month on the tax unpaid at the start of each month. Months one and two are charged on $10,000, or $50 each. The $4,000 payment counts starting with month three, which begins June 16, so months three and four are charged on $6,000, or $30 each. Failure to pay totals $160.

Failure to file is computed on the $10,000 unpaid at the due date, because the May 20 payment came after it. Four months at 5 percent is $2,000 gross. Under IRC 6651(c)(1), subtract the $160 of failure to pay for the four overlapping months, and the failure-to-file penalty is $1,840. Together the two penalties are $2,000, exactly 20 percent of the original $10,000. The partial payment shifted dollars from one penalty to the other but did not lower the combined total, because while both penalties run, the combined rate is pinned at 5 percent of the due-date balance. What the payment did do is stop interest on $4,000 from May 20 forward.

How the overlap shows up on a transcript

On an account transcript, the failure-to-file penalty usually posts as a single assessment with the return, and the failure-to-pay penalty posts in pieces as notices go out. The offset is not shown as its own line. You see the net failure-to-file amount, already reduced. That is why hand-checking it requires the month-by-month failure-to-pay figures for the months the return was late.

A quick test: if the return was filed in month three with nothing paid, the failure-to-file penalty should be 13.5 percent of the tax unpaid at the due date, not 15 percent. If the transcript shows 15 percent, either the IRS did not apply the offset or some of the tax was not subject to failure to pay, for example because it was paid before the due date. In month five or later, the figure to look for is 22.5 percent. Any number above those benchmarks, on a balance with no payments, deserves a question.

And remember the floor. For an income tax return more than 60 days late, the net figure cannot fall below the minimum penalty, $525 for returns required to be filed in 2026. On small balances the benchmark percentages give way to that dollar figure, or to 100 percent of the tax if that is less.

The bottom line

Late filing and late paying together cost 5 percent a month for the first five months, then half a percent a month after that, up to 47.5 percent of the tax. The first five months are where the damage happens. File the return now, even if the check comes later. If you are staring at a notice and the penalty lines do not add up, get someone to rerun them.