Credit & Consumer Law

In Duplum Rule

A common law rule, codified in the National Credit Act, that prevents the unpaid interest on a debt from exceeding the capital amount of the debt outstanding at the time of default.

Legal Definition

The in duplum rule (from the Latin "double") limits the accumulation of interest on a debt. Once unpaid interest equals the outstanding capital, interest stops running. The NCA codifies this rule in section 103(5): the total amount of charges, fees, and interest that may be charged may not exceed the unpaid balance of the principal debt.

📖 Constitutional / Statutory Basis: Section 34 (access to courts — consumer debt relief)

Practical Example

You borrowed R10,000. You defaulted when R8,000 was outstanding. Interest cannot exceed R8,000 in total, making the maximum debt R16,000 (capital R8,000 + interest cap R8,000).

Frequently Asked Questions

Does the in duplum rule apply to all debts in South Africa?

The common law in duplum rule applies to all interest-bearing debts. The NCA version (section 103) applies specifically to credit agreements governed by the NCA.

Does paying part of the debt restart the in duplum cap?

Yes — a partial payment reduces the outstanding capital, which also reduces the cap. The double cannot exceed the outstanding principal at any given time, not the original loan amount.

Related Terms

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