Free tool
Late payment interest calculator.
Work out days overdue and simple interest on an unpaid invoice. Runs in your browser. Nothing is sent anywhere.
Interest = amount x annual rate x days overdue / 365 (simple interest). You can usually only charge interest on an invoice if the rate was agreed in your contract or terms. Court reference rates below are shown as benchmarks only.
General information only, not legal or financial advice. Every business and every debt is different. For advice on your situation, talk to a lawyer, your accountant or your state small business commissioner. This calculator gives an estimate using simple interest at a single rate. Court rates change every six months and courts have discretion.
Days overdue checker
Where the reference rates come from
- Federal Court: pre and post-judgment interest rates: for 1 July to 31 December 2026 the Federal Court table lists an RBA cash rate of 4.35%, pre-judgment interest of 8.35% (cash rate plus 4%) and post-judgment interest of 10.35% (cash rate plus 6%). The rate resets on 1 January and 1 July.
- Supreme Court of Victoria: penalty interest rates: the penalty interest rate fixed under the Penalty Interest Rates Act 1983 (Vic) has been 10% per annum since 1 February 2017.
- RBA cash rate target: the base for court rates in most jurisdictions.
Rates checked 14 October 2026. Always check the current rate on the official site. Other states and courts publish their own rates and rules, so if your matter is in another court, use that court's published rate or your contract rate.