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Late Payment Interest / Fee Calculator

Estimate the interest portion of an overdue balance before you prepare a reminder, follow-up, or updated invoice.

Estimate overdue interest

This tool uses simple daily interest from the invoice principal, annual rate, and number of days overdue. It does not decide whether a fee is allowed.

Used for display only. No currency conversion is performed.

Estimated Interest Accrued0.00
Estimated New Total Owed0.00
How this is calculated: Interest Accrued = (Principal × (Annual Rate / 100) / 365) × Days Overdue.
Important: This calculator is for estimation only. Late fees, interest, collection charges, and reminder wording may be limited by local law or by the written agreement with your client. Confirm your terms before charging a late fee.

How To Use The Late Payment Calculator

Use this calculator when an invoice is overdue and you want to estimate a possible late fee or interest amount before sending a reminder. Enter the overdue balance, the agreed annual rate or fee basis, and the number of days late. The calculator gives you a simple estimate only; it does not decide whether a fee is allowed.

Late fees should match the agreement you gave the customer and the rules that apply in your location. When in doubt, send a polite reminder first and keep the wording factual.

  • Check the original invoice terms before using any fee.
  • Use the unpaid balance, not the original total if partial payment was received.
  • Keep reminder language professional and avoid threats or confusing math.
  • Save a copy of the invoice, reminder, and any payment response.

Calculator FAQ

Can I charge a late fee on any invoice?

Not always. Late fees may depend on your written terms, customer agreement, industry, and local rules.

Should I send a reminder before adding a fee?

Often yes. A polite reminder can resolve the issue without escalation.

Does this calculator collect my invoice data?

No. It runs in your browser and does not store your invoice details.

Payment and follow-up resources

Late payment reminder guideWrite a polite follow-up before escalating.Reminder templateUse a simple structure for overdue balances.Payment terms examplesSet clearer expectations before work begins.
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