Filing Taxes Late After an Extension: What to Do This Week

If you’re going to be filing taxes late after an extension, do three things this week: file whatever is complete by Thursday, October 15, pay an estimate of what you owe the same day, and set up a payment plan for the rest. Filing stops the failure-to-file penalty, which is 5% of the unpaid tax per month. Paying stops most of the interest and the smaller failure-to-pay penalty. A payment plan turns the balance into a monthly amount instead of a notice.

We run an accounting firm, and by this point in October the owners still open fall into one of three situations. Each has a right move, and none of them is “wait until it’s perfect.”

Situation one: the return is done, and you owe more than you can pay

This is the most common and the least serious. The return is finished, the number is real, and it’s bigger than the account can cover this week.

File it anyway, on time. The failure-to-file penalty is the one that hurts, ten times the failure-to-pay rate, and filing on October 15 with a balance due stops it completely.

Pay what you can with the return. Every dollar paid now stops accruing the failure-to-pay penalty and interest. A partial payment is not a problem. An unfiled return is.

Set up a payment plan online the same day. Most individuals with a total balance under $50,000 can set up an installment agreement on the IRS website in a few minutes, without talking to anyone. Businesses have a lower online threshold; your preparer can tell you whether you qualify or need to call. The plan doesn’t stop interest or the failure-to-pay penalty, but the penalty rate is reduced while a plan is in place, and the IRS stops sending escalating notices.

Then move on. A filed return with a payment plan is a normal account status at the IRS. It’s not a mark against you.

Situation two: one item is still open

The return is complete except for one number. A K-1 from a partnership that’s also late. A loan balance the lender hasn’t confirmed. A cost basis on something you sold. Everything else is done.

File with the best number. Ask your preparer for the most defensible estimate of the open item, file the return with it on time, and keep a note in the file explaining what it was and why. If the final figure comes in and it moves the tax materially, amend. If it moves the tax by a rounding error, don’t.

The alternative, waiting for the number and filing late, costs 5% of the entire unpaid balance per month, not just the tax on the open item. For a return with a meaningful balance due, one open item is almost never worth a late filing. An amended return is a second engagement and a second look from the IRS, but that’s usually cheaper than the penalty, and often it’s never needed.

This is a math question. Ask your preparer to put dollars on both paths, and take the cheaper one.

Situation three: the books were never closed

The 2025 books don’t exist in usable form. A bank feed nobody categorized, or a shoebox, or a bookkeeper who stopped answering in April. The return can’t be finished by Thursday because there’s nothing to finish it from.

Pay an estimate now. Your preparer can build a rough number from bank deposits, known payroll, and known large expenses. Pay it by October 15. It won’t be exact, but it stops the failure-to-pay penalty and interest from running on most of the balance, and it means that when the return is filed late, the failure-to-file penalty is calculated on whatever small balance remains, not on the whole year’s tax.

Start the cleanup this week. Not after the holidays. Cleanups go faster than owners expect when they run in the right order: the bank’s own statements read line by line, duplicates removed, categorization by rule, every balance tied to a lender or a payroll report, one question list. We closed four full years of restaurant books in under ten hours of staff time before September 15 this year. Yours can be done in weeks, priced as a fixed fee from a two-hour diagnostic.

File in November. Late, with a penalty on a small balance, from real books. That’s a much better return than a guessed one filed on time and amended twice.

How do I set up an IRS payment plan for my business?

Online if the balance qualifies, by phone or through your preparer if it doesn’t. You’ll choose a monthly amount and a payment date, and the IRS will want it set up as a direct debit for most plans. Three things to know: interest and a reduced failure-to-pay penalty continue until the balance is zero, so pay it off early if you can; you have to stay current on this year’s estimates while the plan runs, or it defaults; and the plan is per taxpayer, so an S-corp owner with a personal balance sets it up personally, not through the company.

The next date

The fourth-quarter individual estimate for 2026 is due January 15, 2027. If you’re on a payment plan for 2025, that estimate is not optional; missing it defaults the plan. And it’s the last chance to keep 2026 from becoming 2025 again.

This year’s scramble should change how that estimate is built. Instead of a fraction of last year’s tax, it should come from this year’s closed books: actual profit through November, a December projection, the tax on the total, minus what’s been paid. That’s a number, not a hope, and it’s the number that makes April 2027 a formality instead of another October.

What a CFO does with this number

A fractional CFO treats a late return as a symptom and asks what it would take to never have one again. The answer is a monthly close, so December 2026 is closed by January 10, the return is a report in February, and the January 15 estimate is built in December from ten closed months and a projection.

The CFO also uses the payment plan in the cash forecast. A monthly installment for the 2025 balance, plus the 2026 estimates, plus payroll and loan payments, all in the 13-week grid, so the low point is visible and the plan never defaults because a payment landed in a tight week nobody saw coming.

Where we come in

If the books are the problem, we start there: a two-hour diagnostic, a fixed fee for the cleanup, the return built from real numbers when it’s done, and a monthly close from then on so the next return runs off closed books in the spring. Tax prep, estimates, and payroll are all in-house, so the estimate in January is built by the people who closed the books it comes from.

If October 15 is Thursday and you’re in any of the three situations above, reach out today. We’ll tell you which move is yours and get the estimate paid before the penalty grows.

Frequently asked questions

What if I can’t file by October 15?
File whatever is complete, pay an estimate of what’s owed to stop most of the interest, and set up a payment plan online the same day.

Is filing late worse than paying late?
Yes; the failure-to-file penalty is 5% of unpaid tax per month, the failure-to-pay penalty is 0.5%.

Can I amend later?
Yes, and for one open item that’s usually better than filing late; ask your preparer before deciding.