Underpayment Penalty Calculator
United States federal tax · tax year 2026 · estimated tax underpayments (Form 2210)
How much is the IRS penalty for missing a quarterly estimated tax payment in 2026?
It is not a flat fine — it is interest on the missed amount at the section 6621 rate, 6% a year to 30 June 2026 and 7% from 1 July, counted day by day until you pay. A $3,000 instalment missed on June 15, 2026 costs $51.70 if cleared on September 15, 2026, and $173.67 if it waits for the return due April 15, 2027 (assuming the 7% rate holds into 2027 — the IRS has not announced next year’s rate).
A missed quarterly payment is not a fine — it is a meter. Interest runs on the shortfall at the section 6621 rate, day by day, until the money arrives. Put in what each instalment should have been, what you actually paid, and when you can clear the rest: this page returns the penalty to the cent, what one more day costs, and what waiting until each of the next few dates would cost instead.
The instalments and the clearing date
The meter stops the day the money arrives — or on 15 April 2027, when the return is due, whichever comes first. A later date is treated as 15 April 2027 because nothing accrues past it.
What you actually paid
Leave a payment at 0 if it never went out. A payment dated on or before its due date was on time and costs nothing; one dated after it was late for those days, and that is charged too. The boxes start on the worked example from our article — a $3,000 instalment missed on 15 June, the other three paid on their due dates. Overwrite them with your own.
What it costs
Instalment by instalment
| Instalment | Due | Shortfall | Status | Penalty |
|---|
Each row is the shortfall times the days it stayed unpaid times the annual rate in force on those days, divided by 365 — the arithmetic on the Form 2210 penalty worksheet. Anything paid after its due date is charged for the days it was late, even though it has since arrived.
What waiting buys
The same shortfall, cleared on later dates. Nothing here is a threat — it is the same meter, read further along.
| Cleared on | Days late | Penalty | More than now |
|---|
† Assumes the underpayment rate stays at 7% into 2027. The IRS sets it quarter by quarter and the 2027 rate has not been announced. Only figures marked † move if it changes; nothing before 1 January 2027 depends on it.
Rates in force: 6% a year through 30 June 2026, 7% from 1 July 2026 (Rev. Rul. 2026-10, Internal Revenue Bulletin 2026-22), and 7% held for October to December 2026.
The dates that matter
- September 15, 2026 — the third 2026 instalment falls due, covering income earned from 1 June to 31 August. It is a separate payment with its own meter — clearing an older shortfall does not settle it.
- January 15, 2027 — the fourth and last instalment for 2026 falls due. From here on, a shortfall can only be cleared, never prepaid into an earlier date.
- April 15, 2027 — the return is due, and the penalty meter stops. Waiting past this date does not add to the underpayment penalty, though ordinary interest and late-payment charges on an unpaid balance are a separate matter.
This is a calculator, not tax advice. United States federal tax only — your state runs its own estimated payments and its own penalties.
- Missed a quarterly estimated tax payment? What it actually costs — the same arithmetic in prose, with the safe-harbour amounts that stop the meter for good and the withholding trick that can repair April in December.
- Quarterly tax calculator — works out what the four 2026 instalments should have been in the first place, from your own profit and filing status.
A web form can price a shortfall you already have. It cannot keep track of what you actually paid across a whole year, or recompute your instalments from the income that really arrived in each period.
- Form 2210 Schedule AI annualisation across all four periods, so a project that lands in August is not billed to you in April — the method that can make a missed June instalment far smaller than a quarter of the year.
- A payment calendar that tracks what you actually paid against what was required, date by date, so you know where you stand before a penalty exists.
- The whole 2026 federal computation behind it — Schedule SE, Form 1040, section 199A and all three safe-harbour tests — with every constant tied to the IRS or SSA document it came from.
How the penalty is actually computed
There is no flat fine. Section 6654 charges interest at the section 6621 underpayment rate — the federal short-term rate plus three points, reset each quarter — and Form 2210 applies it as simple interest: the underpayment, times the number of days it stayed unpaid, times that rate, divided by 365. The instructions put it in one line: “The penalty is figured for the number of days that each underpayment remains unpaid.”
Two things follow. A payment stops the clock on the day it lands, not on the next quarterly date, so paying early in a quarter is worth exactly the days it saves. And each instalment carries its own meter: clearing a missed June payment does nothing about a September one. This page runs the day count for all four separately and adds them up, splitting each span at the quarterly rate boundaries.
What this page does not do
It computes one thing well and refuses to guess at the rest:
- United States federal tax only, and only for tax year 2026. State estimated tax has its own rules, its own dates and its own penalties.
- It does not work out what your instalments should have been — bring that figure with you, or get it from our quarterly tax calculator.
- It uses the flat quarter method. If your income was lumpy, Form 2210 Schedule AI can make an early instalment much smaller, and that is a workbook job, not a web-form job.
- It does not model the waiver boxes on Form 2210, withholding credited a quarter to each date, or anything that happens after the return is filed.
Questions people actually ask
How much is the IRS underpayment penalty for 2026?
It is a rate, not an amount: 6% a year through 30 June 2026 and 7% from 1 July, applied to what you underpaid for the days you underpaid it. On a $3,000 instalment missed on 15 June, that is about 58 cents a day — $51.70 if you clear it on 15 September, $173.67 if it waits for the April return. The figure scales linearly, so a $6,000 miss costs exactly twice each of those.
Is there a penalty if I pay a few days late?
Yes, but a tiny one, and that is the point of showing the daily figure. Five days late on a $2,000 instalment at 7% is about $1.92. There is no threshold you cross and no letter that arrives; the charge simply exists and is added up on Form 2210 with your return.
Does the penalty keep growing forever?
No. An instalment's meter runs until you pay it or until the return's due date — 15 April 2027 for tax year 2026 — whichever comes first. After that the underpayment penalty is fixed. An unpaid balance on the return itself then attracts ordinary interest and a failure-to-pay charge, which are different animals and not modelled here.
Why is the 2027 part of the answer marked with a dagger?
Because the rate for 2027 has not been announced. The IRS sets it quarter by quarter, and any clearing date after 31 December 2026 depends on a rate nobody has published yet. We assume it holds at 7%, mark every figure that rests on that assumption, and leave the rest of the page free of it — rather than printing a number that quietly pretends to know.
Does this calculator store what I type?
No. It runs entirely in your browser, keeps nothing, sends nothing, and asks for no account or email address. Close the tab and the numbers are gone.
