Quarterly Tax Catch-Up Calculator
Missed a quarter — or three? Work out the payment that gets you back on the safe harbor, and see what the quarters you skipped have already cost.
Business income minus business expenses — your full-year estimate.
Everything you've sent the IRS toward 2026. Zero is a common answer.
Optional.
Optional.
From last year's 1040.
Sets the 110% rule.
Behind on quarterly taxes? Here's what to send.
If you've realized in the middle of the year that estimated tax payments applied to you all along, this calculator gives you the one number you actually need: what to send by the next deadline to get back on track. Enter your expected profit, anything you've already paid, and last year's tax, and it works out the catch-up payment — plus an honest figure for what the quarters you missed have already cost.
The arithmetic most people get wrong is the split. Your catch-up payment is not the annual number divided by four. By September 15 three of the year's four installments are already due, so you owe 75% of the required annual total, less whatever you've paid. Send a single quarter's worth and you're still two quarters behind.
Why the catch-up payment isn't your annual number ÷ 4
The IRS expects your required annual payment in four installments, due April 15, June 15, September 15, and January 15. Those installments are cumulative: by the September deadline, three of them have come due, so the amount you should have paid by then is 75% of the annual total — not 25%.
That's why this calculator asks which deadline you're paying. Paying one quarter's worth in September when you've paid nothing since April leaves you 50% short, and the shortfall keeps accruing interest until you close it.
The September 15 deadline, specifically
The third 2026 installment is due Tuesday, September 15, 2026, and it covers income you earned from June 1 through August 31. It is the last deadline of the year that still gives you room to fix things — the fourth isn't until January 15, 2027, by which point the year is over. If a due date lands on a weekend or a legal holiday it rolls to the next business day; September 15, 2026 is a Tuesday, so it doesn't move.
What the quarters you already missed will cost
Less than most people fear. The underpayment penalty is not a fine — it's interest on the shortfall, running from each missed deadline until you pay, at a rate the IRS resets quarterly. For 2026 that rate has been 7% in the first quarter, 6% in the second, and 7% in the third.
The catch is that it's charged per period. A large payment in September is credited in September; it does not reach back and fix April. That's what the second box in the results shows — a cost that's already sunk, separate from the payment that's still in your control.
Aim at the safe harbor, not at a year you can't predict
You have two ways to avoid the penalty: pay 90% of what you'll owe this year, or pay 100% of what you owed last year — 110% if your prior-year AGI topped $150,000. The second is almost always the better target for a freelancer, because it's a fixed number you already know rather than a projection of a year that hasn't finished. Enter your 2025 total tax and this calculator will use whichever of the two is lower.
If you have W-2 income, there's a second lever
Estimated payments are credited on the day you make them, but tax withheld from a paycheck is credited evenly across all four periods by default — no matter when it was actually withheld. That means extra withholding late in the year can reach backwards and cure an earlier shortfall in a way a September estimated payment cannot. If you or a spouse has a W-2, that's often the cheaper fix.
Frequently asked questions
I haven't paid anything all year — can I just pay it all in September?+
You can, and you should. Paying the full catch-up amount by September 15 gets you current through three of the four installments and stops interest accruing on the shortfall. You'll still owe a penalty on the April and June quarters, because those payments were late — but it's interest, not a fine, and it stops the day you pay.
Does paying extra in September fix the quarters I missed?+
No. The IRS credits an estimated payment on the date you make it, and the underpayment penalty is calculated per period. A September payment can't retroactively fund the April installment. Pay anyway — the penalty keeps growing until the shortfall is closed.
How much is the penalty for missing a quarterly payment?+
It's interest on the amount you were short, running from that quarter's deadline until you pay. The 2026 rate has been 6–7% annually, so a $3,000 shortfall left unpaid for four months costs roughly $70. Unpleasant, but rarely the catastrophe people brace for.
What if this is my first year freelancing and I have no prior-year tax?+
Then the 100%-of-last-year safe harbor isn't available to you, and the calculator falls back to 90% of your projected 2026 tax. Keep your profit estimate honest and revisit it as the year goes on — if income climbs, the required amount climbs with it.
Is September 15 the last chance to fix my 2026 taxes?+
It's the last quarterly deadline of the calendar year — the fourth isn't until January 15, 2027. It isn't literally your last chance, but every month you wait adds interest, and if you have W-2 income in the household, adjusting withholding before year-end is the only move that can still fix earlier quarters.
Stop running the numbers by hand.
TaxClover keeps every figure on this page current automatically — and reminds you before each quarterly deadline. Free while we're in beta.