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Estimated Tax Penalty Calculator

Missed or underpaid a quarter? Estimate the IRS underpayment penalty — calculated quarter by quarter at the current 2026 interest rate.

What you owed & paid
$

Your safe-harbor amount — split into four equal quarters below.

Required per quarter: $4,000
$
$
$
$
Estimated underpayment penalty
$692
on $16,000 of underpaid estimated tax, at the current ~6.5% IRS rate.
Q1 2026 · $4,000 short · 365d$260
Q2 2026 · $4,000 short · 304d$217
Q3 2026 · $4,000 short · 212d$151
Q4 2026 · $4,000 short · 90d$64
Total estimated penalty$692
The penalty accrues from each missed deadline until you pay — so paying sooner, even late, costs less than waiting. There's no penalty on a quarter you funded in full.
A planning estimate built from 2026 figures — not a filed return or tax advice. Confirm anything important with a qualified tax professional.

How the underpayment penalty works

The IRS estimated-tax penalty isn't a flat fine — it's interest. When a quarterly payment is missed or short, interest accrues on the shortfall from that quarter's deadline until the date you pay, at a rate the IRS resets each quarter. Because it's interest, paying late is always cheaper than not paying: the meter stops the day you catch up.

The 2026 interest rate

For individuals, the IRS underpayment rate is 7% for the first quarter of 2026 and 6% for the second. The rate equals the federal short-term rate plus three percentage points and is announced quarterly. This calculator applies a blended current rate as a planning estimate.

Why this is an estimate

The official calculation lives on IRS Form 2210 and is genuinely fiddly — it applies the exact rate in force during each sub-period and can shift an overpayment in one quarter forward to another. This tool computes a clean per-quarter estimate so you know the rough cost; your filed return or tax software produces the precise figure.

Frequently asked

How much is the IRS penalty for not paying quarterly taxes?+

It's interest on the underpaid amount, currently around 6–7% annually, accruing from each missed deadline until you pay. The exact figure depends on how much you were short and how long the shortfall went unpaid.

Can I avoid the penalty entirely?+

Yes — meet a safe harbor. Pay 90% of this year's tax or 100% of last year's (110% if prior-year AGI topped $150,000) and no penalty applies. The safe harbor calculator sizes that payment for you.

Should I still pay if I already missed a quarter?+

Absolutely. The penalty is interest that keeps accruing until the shortfall is paid. Paying as soon as you can — even between deadlines — stops the meter and limits the cost.

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