When loans spiral: Can interest legally exceed the principal?
By Kenneth Mwenda, March 14, 2026Many borrowers worry that interest can grow uncontrollably, leaving them with debts far higher than the amount they originally borrowed. Legal rules exist to prevent this, but their application can be complex depending on the loan type and governing law.
In Kenya, the in duplum rule protects borrowers by capping interest at the principal. Once interest matches the original loan amount, it stops accruing.
“There is a legal principle called the in duplum rule, where a financial institution is barred from recovering or charging interest that exceeds the principal,” James Itaya, a financial commentator, explained. This rule prevents borrowers from falling into endless debt spirals.
Consider a business that borrows Ksh500 million to fund a major development. Over several years, unpaid interest and fees could push the total debt to Ksh1.2 billion. Without safeguards like the in duplum rule, the borrower could face more than double the original sum, even if the project has not yet generated profit. This can lead to severe financial pressure and risk of losing assets.
However, applying the rule is not always straightforward. Some loans are governed by international or regional agreements, which may override local caps. In Kenya, the Central Bank of Kenya sets the base lending rate, which guides how financial institutions manage credit.
When in duplum fails
Contracts that follow foreign laws, such as English law, can allow interest to accumulate beyond the principal. Experts warn that borrowers must fully understand the terms before signing. A lender who refuses a full cash settlement from a reputable institution is not always seeking repayment – they may prefer asset forfeiture.
Borrowers can protect themselves by requesting clear statements of account and seeking legal clarification when debts rise unexpectedly. Courts have examined whether interest has breached the in duplum limit, and judges may interpret the law differently depending on the case.
Transparency and ethical conduct by lenders are also critical. Unethical demands or delays by lenders can put borrowers in difficult situations, especially when funds are withheld or officials act outside agreed-upon terms. Bribery, coercion, or refusal to release agreed-upon funds can worsen financial disputes.
Despite these challenges, borrowers have legal recourse. Laws such as the in duplum rule exist to keep debt manageable.
Protecting borrowers from debt
The principle exists to stop interest from turning a reasonable loan into an endless liability. Borrowers who understand the protections in place are better positioned to defend their rights and avoid unnecessary losses.
The question of whether interest can exceed principal highlights broader issues in lending. Large loans carry risks for both parties. Borrowers need to carefully read contracts, monitor interest accumulation, and understand applicable laws. Lenders must act transparently and adhere to legal limits to prevent disputes.
Financial literacy plays a key role. Borrowers should understand how interest compounds and what total exposure may look like over time. Knowing the rules, including limits under local or international law, can prevent loans from becoming unmanageable.
The in duplum rule demonstrates the balance between lender rights and borrower protection. It ensures fairness and prevents excessive financial pressure. Still, each loan’s context matters, and borrowers must remain vigilant.
Ultimately, while interest can accumulate quickly, safeguards like the in duplum rule exist. Once interest equals the principal, it should stop growing. Understanding these protections can make the difference between manageable debt and a financial crisis.