How much arrear interest can you actually claim on an overdue debt? Enter the capital, the rate and the day the debt fell due. The calculator runs the interest, then applies the in duplum rule — unpaid interest may never exceed the capital still outstanding — and tells you the date interest stops running. For a credit agreement it also measures the default charges against section 103(5) of the National Credit Act.
Enter the capital, the rate and the day the debt fell due. The calculator works out the arrear interest, then applies the in duplum rule: unpaid interest may never exceed the capital still outstanding. It will tell you the date interest stops running, and for a credit agreement it measures the default charges against the wider cap in section 103(5) of the National Credit Act.
Most debts are governed by the common-law rule. A credit agreement carries a wider statutory one.
| Rule | What it caps | Authority | Note |
|---|---|---|---|
| In duplum | Unpaid interest | Common law | Arrear interest may never exceed the capital still outstanding. Once it does, interest stops until capital is paid down. Applies to any debt bearing interest. |
| Statutory in duplum | All default charges | NCA s 103(5) | Under a credit agreement, interest plus initiation and service fees, credit insurance, default administration charges and collection costs accruing during default may not exceed the unpaid balance of the principal debt at the time of default. |
| Prescribed rate | The rate itself | Act 55 of 1975 | Where the parties agreed no rate, interest runs at the rate prescribed by the Minister. The rate changes, and a long-running debt may cross more than one rate. |
| Prescription | The whole claim | Act 68 of 1969 | Separate from interest: most debts prescribe three years after they fall due, and a prescribed debt cannot be enforced at all. Check the date on the prescription calculator. |
A common-law rule that unpaid arrear interest may never exceed the capital still outstanding. Once the interest a debtor owes equals the unpaid capital, interest stops running until some of the capital is paid off. It protects the debtor from a debt that grows without limit.
Yes, and in both directions. The ceiling is the capital still outstanding, so paying capital down lowers the ceiling as well as slowing the accrual. Paying arrear interest off frees room for interest to run again.
That was considered in Standard Bank of South Africa Ltd v Oneanate Investments (Pty) Ltd 1998 (1) SA 811 (SCA), where the court held the rule does not restrain interest during litigation the way it does before. This calculator applies the cap flatly and does not model what a court may allow from service of summons, so take advice on a matter already in litigation.
For a credit agreement it caps more than interest. The charges that accrue while the consumer is in default — interest, initiation and service fees, credit insurance, default administration charges and collection costs — may not together exceed the unpaid balance of the principal debt at the time of default. Tick the credit agreement box and the calculator measures the costs against that limit too.
The rate prescribed under the Prescribed Rate of Interest Act 55 of 1975. The Minister changes it from time to time, so this page asks you for the rate rather than printing a figure that may be out of date. Confirm the rate in force for the period you are claiming, and note that a different rate may apply to different stretches of the same debt.
No. It is simple interest on one capital amount at one rate, which is how arrear interest is usually claimed, and it is a working aid rather than legal advice. A debt with part payments, rate changes or compounding needs a proper reconciliation. AttorneyOS does that on the collections desk, applies the in duplum cap to every debt automatically and warns before prescription. The first month is R1.
Once the in duplum cap is reached, waiting costs you. A listed attorney can demand, summons or attach before the claim prescribes.
Find an attorney to recover itThe AttorneyOS collections desk applies the in duplum rule to every debt as it runs, tracks capital, interest and costs separately, and warns before prescription.