Tax penalty and interest calculators
Find out what a late return, an unpaid balance or missed estimated payments cost, for an individual or a business. Pick the return, enter the amounts and dates, and see the penalties and interest line by line.
Prepared by Prem Tax and Accounting Corp. Last checked against official sources on November 11, 2026.
Individuals (Form 1040)
Federal late filing, late payment, interest and the estimated tax penalty, plus a state-by-state tab for all 50 states and DC.
Read →S corporations (Form 1120-S)
The per-shareholder late-filing penalty and the penalties and interest on tax the corporation itself owes.
Read →Partnerships (Form 1065)
The per-partner late-filing penalty and the penalty and interest on entity-level tax.
Read →C corporations (Form 1120)
Late filing, late payment, the Form 2220 estimated tax penalty and interest, with the large corporation rate.
Read →How the penalties work
- Late filing: 5% of the unpaid tax for each month or part of a month the return is late, up to 25%. The 5% is cut to 4.5% for months when the late-payment penalty also applies.
- Late payment: 0.5% of the unpaid tax for each month or part of a month, up to 25%. It is 0.25% under an installment agreement on a timely filed return and 1% after a notice of intent to levy.
- Interest: charged from the original due date at the IRS underpayment rate, compounded daily and reset every quarter. The 2026 rates are 7%, 6%, 7% and 7%.
- Entities: a partnership or S corporation owes a monthly penalty for each partner or shareholder when its return is late, even if no tax is due. For returns due in 2026 it is $255 per owner per month, up to 12 months.
What the calculators leave out
They do not figure the accuracy-related or fraud penalties, foreign information return penalties, or the annualized income method for estimated tax. See the IRS letter guide if you already have a notice, or book a 10-minute call.
Common questions
Are these the amounts the IRS will bill?
No. They are estimates built from the published rules and the IRS interest rates for each quarter. The IRS bills its own figure, which can differ for reasons such as an installment agreement, an abatement or a payment it applied in a different order.
Is anything I enter stored?
No. The math runs in your browser, and nothing you type is sent to us.
Can you check a notice I already received?
Yes. Send us the notice and we check the math, look for first-time abatement or reasonable-cause relief, and respond to the IRS or the state for you.
Official sources
- IRS: Quarterly interest rates
- IRS: Failure to file penalty
- IRS: Failure to pay penalty
- IRS: Underpayment of estimated tax by individuals penalty
Let's talk about your taxes, your business, your plans.
Tell us what you need and we will get back to you quickly. There is no pressure: just a friendly conversation and a clear next step.
4260 Westbrook Dr, Suite 107
Aurora, IL 60504
Monday to Friday, 9:00 am to 5:00 pm, by appointment. Saturday and Sunday by appointment when needed.