Late Payment Interest Calculator
What an overdue invoice has actually cost you — interest by the day, plus any fixed compensation you are entitled to charge.
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How it works
Late payment interest normally runs from the day after the due date to the day payment arrives, charged daily on the outstanding amount. Many jurisdictions also entitle a supplier to a fixed compensation sum per invoice on top of the interest.
The figure is worth calculating even when you do not intend to charge it. It puts a number on what extended payment terms cost you, which is a far more persuasive thing to raise in a collections conversation than a general complaint about slow payment.
Interest = amount × annual rate × days overdue ÷ 365
- Days overdue — from the day after the due date until payment
- Annual rate — contractual, or the statutory rate where one applies
- Compensation — a fixed sum per late invoice, where the law allows it
Worked example
A 480,000 invoice due 2026-04-15, paid 2026-08-02, at 12% with 5,000 compensation
Inputs
Results
109 days late on one invoice costs 22,201 — roughly 4.6% of its value, and that is before the cost of chasing it.
Frequently asked questions
When does interest start running?
From the day after the due date in most regimes, not from the invoice date. If no due date was agreed, statutory schemes commonly default to 30 days after delivery or invoice receipt.
What rate can I charge?
Whatever your contract states, if it states one. Where it does not, many jurisdictions set a statutory rate — often a reference rate plus a margin of several points. Enter the one that applies to you.
Should I actually charge it?
That is a commercial judgement, and many suppliers never invoice it. Calculating it anyway is still worthwhile: it quantifies what slow payment costs, which is the strongest argument for tightening terms.
Is my data sent anywhere?
No. The calculation runs entirely in your browser. Nothing you type is transmitted to us or stored.
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