Cost & contract

Interest rates explained: flat vs reducing balance

Updated 2026 · English

Why the number on the advert is not the whole story

Loan adverts in Nigeria love to lead with a small-looking percentage. But the number you see is only half the story: it depends on how that percentage is applied. Two lenders can advertise the same rate, yet one can cost you far more than the other, depending on whether they use flat or reducing-balance interest. Understanding this single difference can save you a surprising amount of money.

Flat interest explained

With flat interest, the interest is calculated on the original amount you borrowed and then divided across the whole repayment period. Even as you pay the loan down, the interest is based on the original figure.

For example, borrow 100,000 naira over 12 months at a flat 2% per month. The flat monthly interest is 2,000 naira. Over 12 months that is 24,000 naira in interest, on top of repaying the 100,000. Your total repayment is 124,000 naira.

Flat interest looks simple, which is why lenders like to quote it. But because you keep paying interest on the full amount even after it is partly repaid, the effective cost is higher than it appears.

Reducing-balance interest explained

With reducing-balance interest, you pay interest only on the amount you still owe at each point. As you repay, the balance falls, so the interest each month falls too.

Using the same example: borrow 100,000 naira over 12 months at 2% per month on a reducing balance. In the first month you pay interest on the full 100,000 (2,000 naira). By month six, the balance is lower, so the interest is lower. Over the year, you pay noticeably less total interest than under flat — often somewhere in the region of half as much for the same advertised rate, depending on the schedule.

Which is more common, and why it matters

Both methods are used in Nigeria. Loan apps and digital lenders frequently quote reducing-balance rates because they sound and cost differently from flat rates. The practical lesson is not to assume one is “better” than the other on the number alone. What matters is the total you repay.

When someone quotes you a percentage, always ask: “Is this flat, or on a reducing balance?” and “How much in total must I repay?”. Those two questions will tell you the real cost better than any advert.

What APR means

APR stands for Annual Percentage Rate. It is a standard way to express the annual cost of borrowing, including interest and many fees, as a single yearly percentage. Because it standardises the calculation, APR is meant to let you compare two very different loan offers fairly.

In Nigeria, quoted annual rates vary widely by lender and by the type of loan, so we will not invent figures. The general principle stands: the lower the APR on a comparable loan, the cheaper it is, and the more clearly a lender shows APR, the more seriously it is treating transparent comparison. Use the APR figure alongside total cost in naira, because fees can hide in the weeds.

Fees are part of the cost

Interest is only one ingredient. Processing fees, insurance, document charges and late fees all add to what you really pay. A loan with a slightly lower interest rate but heavy fees can end up costing more. When comparing, look at the total cost, not just the interest rate. Our loan comparison framework is built around exactly this idea.

How to work out the true cost

1. Get the amount you will actually receive.
2. Get the exact total you must repay.
3. Subtract step 1 from step 2 to see the total cost in naira.
4. Add any upfront fees you already paid.
5. Compare that final number across lenders, not the advertised percentages.