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Late payment calculator
Late payment interest is the invoice amount times the annual rate, prorated for the days it is overdue. This calculator shows the interest, any flat fee and the new total.
Result
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Formula
Interest = Amount × (Annual rate ÷ 100) × (Days late ÷ 365)
Total = Amount + Interest + Flat fee How it works
Simple interest, prorated daily — not compounded. The rate is one YOU supply from your own terms. This is arithmetic, not legal advice: statutory late-payment entitlements vary by country and contract, so check what applies to you.
Example
5,000 unpaid for 45 days at 8% a year = 5,000 × 0.08 × 45/365 = 49.32 interest, so 5,049.32 is now due.
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