Late Fee & Interest Calculator
Work out a fair late fee or overdue interest on an unpaid invoice and see the new balance due. Free and instant.
Invoice
Late fee
Interest is charged pro-rata: amount × annual rate × days ÷ 365. Keep within the legal cap for your region.
New balance due
$1,006.58
An estimate only. Late fees and interest are capped by law in many places — check your local rules and contract before charging.
Add late fees automatically
SnapBilly flags overdue invoices and chases them for you.
- Auto overdue detection
- Reminders on a schedule
- Late-fee line items
- Payment tracking
- Unlimited invoices
- Client portal
Interest or flat fee
Charge pro-rata interest, a flat late fee, or both — whatever your contract states.
Pro-rata by days
Interest is calculated for the exact number of days an invoice is overdue.
See the daily cost
Know how much interest is accruing each day the invoice stays unpaid.
Stay compliant
A clear estimate to compare against the legal cap in your region.
How it works
- 1
Enter the overdue invoice amount and how many days late it is.
- 2
Choose how you charge: annual interest, a flat fee, or both.
- 3
Set the interest rate and/or flat fee amount.
- 4
Read the late fee and new balance due — then add it to your invoice or reminder.
Frequently asked questions
How do I calculate interest on an overdue invoice?
Multiply the overdue amount by the annual interest rate, then multiply by the number of days overdue divided by 365. For example, $1,000 at 8% for 30 days is 1000 × 0.08 × 30/365 ≈ $6.58.
What is a reasonable late fee?
Common practice is a flat fee (e.g. $25–$50) or monthly interest of 1–2% (roughly 12–24% annually). Many jurisdictions cap the maximum you can charge, so check local rules and make sure your fee is stated in your contract or invoice terms.
Can I charge both interest and a flat fee?
Yes, if your agreed payment terms allow it. Select “Both” to add a fixed fee on top of accruing interest. Always disclose the policy up front so it’s enforceable.
Is this late fee calculator legal advice?
No. It’s an estimate to help you apply your own terms. Late-fee and interest limits vary by country, state and contract, so confirm the rules that apply to you before charging.