Calculate interest on outstanding debts.
What is Mora Interest?
Mora interest (from the Latin mora, meaning delay) is the interest a creditor is legally entitled to claim when a debtor fails to pay a sum of money by a specific due date.
In South African law, if you are owed money and there is no specific interest rate mentioned in your contract, or if no written contract exists, you are still entitled to charge interest on the outstanding amount under the Prescribed Rate of Interest Act 55 of 1975.
Key Concepts:
- Mora Ex Re: Interest begins automatically if a specific date for payment was set in a contract and the debtor missed it.
- Mora Ex Persona: If no date was set, interest begins only after a formal Letter of Demand is sent to the debtor, giving them a reasonable time to pay.
- The Prescribed Rate: This is the legal “default” rate set by the Minister of Justice. It is currently linked to the South African Reserve Bank (SARB) Repo Rate plus 3.5%.
How to Use the Mora Interest Calculator
To get an accurate calculation of the interest owed to you, follow these steps:
- Enter the Principal Amount: The original amount of the debt (excluding any previous interest).
- Select the Start Date: This is the date the debtor fell into mora. (Either the date the payment was due or the date the Letter of Demand expired).
- Select the End Date: Usually “Today” or the date you expect the payment to be made.
- Rate Type: The calculator uses the Prescribed Rate of Interest applicable at the time the debt became due.
- Note: In South African law, the rate that applies on the day the debt becomes due remains fixed for the duration of that debt, even if the Minister changes the rate later.
Current Prescribed Rate of Interest
As of September 1, 2025, the Prescribed Rate of Interest in South Africa is 10.5% per annum.
| Effective Date | Prescribed Rate (p.a.) |
| 1 Sept 2025 – Present | 10.5% |
| 1 July 2023 – 31 Aug 2025 | 11.75% |
| 1 May 2023 – 30 June 2023 | 11.25% |
(Note: Always ensure you are using the rate applicable to the date your debtor first defaulted.)
Frequently Asked Questions
Can I charge mora interest if I don’t have a written contract?
Yes. Mora interest is a common-law right. If a person owes you a liquidated sum (a specific, fixed amount) and is late paying, you are entitled to interest even without a prior agreement.
What is the “In Duplum” Rule?
In South Africa, the In Duplum rule protects debtors by stating that interest stops running once the total amount of unpaid interest equals the outstanding capital (principal) amount. Our calculator takes this legal limit into account.
Do I need a lawyer to claim mora interest?
For small claims, you can calculate the interest yourself and include it in your demand. However, for large commercial disputes or complex litigations, it is always recommended to consult a legal professional to ensure your dates and rates are legally sound.