Late-payment interest calculator

Work out the interest a customer owes on an unpaid invoice at the prescribed rate (10,75% from 1 November 2026) or your contract's rate, per day, with the in duplum limit. Free.

The rules in short

• Where a contract sets no rate, the prescribed rate applies: the repo rate plus 3,5 percentage points (Prescribed Rate of Interest Act).
• The rate is the one in force when interest began to run.
• Unpaid interest stops once it equals the unpaid amount (the in duplum rule). Credit agreements have their own limits under the National Credit Act.

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General guidance only, not legal, tax or compliance advice. Requirements, fees and processes change: confirm each item with the official body before you act. SignalLedger is an independent private platform, not a government website. Checked 19 October 2026. How we check our information.