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Late Fee Calculator

Work out what a late-paying client actually owes — monthly, annual or flat-fee rules, calculated live. Free forever, anywhere in the world.

Late Fee Calculator

Results update live as you type. Nothing leaves your browser.

Your Numbers
Monthly fees use a 30-day month; annual fees use a 365-day year. A flat fee is charged once, however many days the invoice is overdue. Always check what your contract — and your local rules — allow before charging a late fee.
Your result
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total due
Overdue invoice amount0.00
Late fee0.00
Total due0.00
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How to calculate a late fee in 3 steps

  1. Enter the overdue amount. Type what the client still owes on the invoice.
  2. Pick your rule. Choose a percentage per month, a percentage per year, or a flat fee — use a preset or type your own rate.
  3. Read the total due instantly. You get the late fee and the new total, with the exact formula shown — ready to put on the invoice or in a reminder.

Why a clear late-fee rule gets you paid

A late fee is not really about the money — it is about the deadline. When an invoice quietly sits unpaid, there is no cost to the client for waiting. A stated rule changes that: 1.5% a month, or a flat fee after 30 days, turns “pay whenever” into a date with a price. The trick is stating the rule before the work starts, in the payment terms on the invoice itself, and then applying it consistently. This calculator gives you the exact number to quote, whether your rule is monthly, annual or flat. Once you have it, add the fee as its own line on the invoice with the free invoice generator, and follow up with the payment reminder generator — a polite reminder with a precise total lands very differently from a vague “just checking in”.

Late fee calculator FAQ

Multiply the overdue amount by the monthly rate, then by the days overdue divided by 30. A $1,000 invoice at 1.5% per month, 60 days overdue, is 1,000 × 1.5% × 60 ÷ 30 = $30.00 in late fees, for a $1,030.00 total due.
Multiply the overdue amount by the annual rate, then by the days overdue divided by 365. A $1,000 invoice at 12% per year, 60 days overdue, is 1,000 × 12% × 60 ÷ 365 = $19.73 in late fees, for a $1,019.73 total due.
A single fixed amount charged once, no matter how many days the invoice is overdue — for example $25 or $50 per overdue invoice. It is simple to explain to clients, but it does not grow with the delay the way a percentage fee does.
Only if your contract or invoice terms say so, and only within what your local rules allow — some places cap late fees or require the rate to be agreed in advance. Put the rule in writing on the invoice before the work starts, not after the payment is already late.
Add it as its own line item on the invoice, labelled as a late fee with the rule you applied — for example “Late fee: 1.5% per month, 60 days overdue”. Use the free invoice generator to create the invoice, then send it with a payment reminder.
Yes — unlimited calculations, no signup, no watermark. Everything runs in your browser; nothing you type is uploaded anywhere.