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Free Penalty Check

Form 2210 Estimated Tax Penalty Calculator

Are you inside the safe harbor? Check in 60 seconds, see what a shortfall is costing you per quarter, and the withholding move that can still fix it.

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Quick Answer

The IRS underpayment penalty is interest in disguise, the federal short-term rate plus 3 points (7% for October through December 2026), charged per quarter on the gap between what you paid and your required annual payment: the smaller of 90% of this year's tax or 100% of last year's (110% if last year's AGI was over $150,000). This tool runs the check, estimates the damage, and tells you whether the year-end withholding rescue can still save you.

Tax planning slots are limited before year-end.

Your Numbers

Example figures, replace with yours

$

Income tax + SE tax, before withholding. Rough is fine, try our SE tax calculator.

$

"Total tax" line from last year's 1040, not your refund or balance due.

Yes bumps your prior-year safe harbor from 100% to 110%.

$

Projected full-year total. Withholding counts as paid evenly all year.

Estimated Payments Made (or Planned) Per Quarter

$
$
$
$

Federal short-term rate + 3%, set quarterly: 7% for October through December 2026. Update it if the IRS announces a different rate for January 2027.

Simplified Form 2210 math: equal quarterly installments, withholding spread evenly, shortfalls assumed unpaid until April 15, 2027. This tool does not run Schedule AI. If most of your income arrived late in the year, the annualized income installment method can produce a much lower official penalty, but only if you file Form 2210 with Schedule AI.

Estimated Underpayment Penalty

$596

Required annual payment: $52,800 (110% of last year's tax) · You've paid/planned $40,000

InstallmentDueRequired (cum. ÷ 4)Cumulative Shortfall
Q1Apr 15, 2026$13,200$3,200
Q2Jun 15, 2026$13,200$6,400
Q3Sep 15, 2026$13,200$9,600
Q4Jan 15, 2027$13,200$12,800
Key Insight

The withholding rescue can still erase this

Withholding counts as paid evenly across the year no matter when it happens. A year-end W-4 boost, a heavily-withheld bonus, or an IRA distribution with high withholding can retroactively cure Q1 to Q3 shortfalls in a way a January estimated payment cannot. This is a standard year-end move we run for clients, and it has a deadline of December 31.

See the Q4 estimated tax payment guide for a worked comparison of paying on January 15 versus withholding in December.

Watch Out

Safe harbor protects you from the penalty, not the bill

Meeting the 100%/110% prior-year target means no penalty even if your income doubled, but the full balance is still due April 15. If this year is much bigger than last, park the difference somewhere liquid and let it earn interest for you instead of the IRS.

Tired of guessing every quarter?

Our planning clients get safe-harbor targets computed at tax time, payments scheduled, a mid-year check, and a year-end withholding true-up.

Book your free 30-minute tax fit call to talk through your next steps.

Tax planning slots are limited before year-end.

Read the Estimated Taxes Guide

Worked example

A 1099 physician who paid $10,000 a quarter against a $60,000 tax bill

A self-employed physician expects $60,000 of total 2026 tax. Last year's total tax was $48,000 and last year's AGI was over $150,000. There is no wage withholding, and the physician paid $10,000 of estimated tax on each of the four due dates.

Inputs

Worked example inputs
Expected total tax this year$60,000
Last year's total tax$48,000
Prior-year AGI over $150,000Yes
Withholding this year$0
Estimated payments$10,000 each quarter
Penalty rate7% annual

Calculator output

Worked example calculator output
Required annual payment$52,800 (110% of last year's tax)
Required per installment$13,200
Q1 cumulative shortfall (due Apr 15, 2026)$3,200
Q2 cumulative shortfall (due Jun 15, 2026)$6,400
Q3 cumulative shortfall (due Sep 15, 2026)$9,600
Q4 cumulative shortfall (due Jan 15, 2027)$12,800
Estimated underpayment penalty$596
Balance still due at filing$20,000

110% of last year's $48,000 is $52,800, which is less than 90% of this year's $60,000, so it sets the target. Each $10,000 payment falls $3,200 short of the $13,200 installment, so the shortfall grows every quarter. Each new shortfall accrues 7% a year from its due date to April 15, 2027.

Methodology

How this calculator works

The calculator runs a simplified Form 2210 regular-method test: it finds your required annual payment, splits it into four installments, and charges the underpayment rate on each installment shortfall until the filing date.

Formulas

  • Required annual payment = the smaller of 90% of this year's tax or 100% of last year's tax (110% if last year's AGI was over $150,000).
  • Each installment requires 25% of the required annual payment. Withholding is credited 25% per quarter; estimated payments are credited in their own quarter, and overpayments carry forward.
  • Penalty = sum of each quarter's new cumulative shortfall x the annual rate x days from that due date to April 15, 2027 / 365.
  • No penalty when this year's tax minus withholding is under $1,000.

Assumptions

  • The default 7% rate is the IRS individual underpayment rate for the quarter beginning October 1, 2026. One rate is applied to the whole period.
  • Any shortfall stays unpaid until April 15, 2027.
  • Last year was a full 12-month tax year with a filed return. Leaving last year's tax blank uses the 90% test only.

What it ignores

  • The annualized income installment method and the election to use actual withholding dates.
  • The no-penalty rule when last year's tax was zero, the $75,000 threshold for married filing separately, and the farmer and fisherman rules.
  • Waivers for casualty, disaster, retirement or disability, and state estimated tax penalties.

Sources

Primary sources

  1. 26 U.S. Code Section 6654: failure by individual to pay estimated income tax: required annual payment, installments, the 110% rule and the $1,000 exception
  2. 26 U.S. Code Section 6621: determination of rate of interest: underpayment rate is the federal short-term rate plus 3 points
  3. IRS IR-2026-98: interest rates remain the same for the fourth quarter of 2026: 7% individual underpayment rate from October 1, 2026
  4. IRS: quarterly interest rates: rates by quarter
  5. Instructions for Form 2210: regular method, annualized income method and waivers
  6. IRS Publication 505: tax withholding and estimated tax: safe harbors and the treatment of withholding as paid evenly
  7. IRS: about Form 1040-ES, estimated tax for individuals: 2026 installment due dates

Written by Bryan Martin, CPA, Managing Partner and Founder of Taxstra. Last reviewed October 20, 2026. Taxstra is a CPA firm serving 1,000+ clients in all 50 states.

Educational, not individualized tax advice.

How the Underpayment Penalty Works

The penalty is computed installment by installment: each quarter you're required to have paid a quarter of your required annual payment (the safe-harbor number), and any shortfall accrues interest-style penalty from that quarter's due date forward. That's why it's tested against the timeline of your payments, not the annual total, and why a January catch-up payment doesn't fix a June miss.

The complete rulebook, who must pay, how to size payments, the annualized method for lumpy income, and the due dates, lives in our estimated tax payments guide. For what to do once a penalty notice has already arrived, see the Form 2210 penalty guide. The last 2026 installment is due January 15, 2027; the Q4 payment guide shows how to size it and how to pay estimated taxes online covers Direct Pay and EFTPS. Check the full deadline calendar so the next installment doesn't sneak up on you.

Common Questions

How is the IRS underpayment penalty calculated?

The IRS applies the published quarterly underpayment rate to each installment shortfall for the period it remains unpaid. The individual rate is 7% for the fourth quarter of 2026. Form 2210 and its worksheet do the official calculation; this calculator provides a simplified estimate.

What is the safe harbor that avoids the penalty?

You owe no underpayment penalty if your timely payments (withholding plus quarterly estimates) reach the smaller of 90% of this year's total tax, or 100% of last year's total tax. 110% if your prior-year AGI exceeded $150,000. There's also a de minimis rule: owe less than $1,000 after withholding and no penalty applies at all.

Can I still fix an underpayment this year?

Often, yes, through withholding. Unlike estimated payments (credited when paid), tax withheld from wages, bonuses, or an IRA distribution is treated as paid evenly through the year, no matter when it happens. A December withholding boost can retroactively cure shortfalls from Q1-Q3. A December estimated payment can't do that; it only stops future accrual.

Is the underpayment penalty deductible?

No. Like all federal tax penalties and interest owed to the IRS, it is not deductible, which makes it strictly worse than a margin loan at the same rate. If cash flow is why you underpaid, borrowing to pay quarterlies is sometimes literally cheaper than the penalty.

Can the penalty be waived?

In limited cases: casualty, disaster, or other unusual circumstances where the penalty would be inequitable; retirement (after 62) or disability in the year the underpayment began, with reasonable cause; and the annualized income method can eliminate the penalty when income arrived late in the year. Waivers are requested on Form 2210, with a real explanation attached.

Why do I have a penalty when I got a refund?

Because the test is quarterly, not annual. Pay nothing all year, then overpay in January, and you can still owe a penalty for Q1-Q3 even though April brings a refund. The IRS charges for the time value of the money it should have had earlier, that's the entire concept of the penalty.

Want estimated payments handled for you?

A free 30-minute call with our team about your needs, how we can help, and whether we are a good fit. Payment calculations, projections and tax advice come after engagement.

Tax planning slots are limited before year-end.

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Make this the last penalty season

Book a free 30-minute call with our team. Tell us what you need, learn how Taxstra handles safe-harbor targets, scheduled payments and year-end true-ups for clients, and see whether we are a good fit. Calculations and advice come after engagement.

Tax planning slots are limited before year-end.

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