Flat Rate vs Reducing Balance: Why a '10% Loan' in Nigeria Really Costs 18%

Two lenders offer you ₦1,000,000 for a year. One says 10%. The other says 18%. The first is the better deal, obviously.

Except it usually isn't — because Nigerian lenders quote interest two fundamentally different ways, and a 10% flat rate and an 18% reducing balance rate cost you almost exactly the same money. If you don't know which one you're being quoted, you can't compare two loans at all, and the number that looks cheaper is very often the expensive one.

The short answer

Reducing balance charges interest only on what you still owe. As you repay, the interest shrinks. This is how mortgages, most bank loans, and every honest APR work.
Flat rate charges interest on the original amount for the whole term, even though you're paying the balance down every month. You're being charged for money you've already given back.
A flat rate is worth roughly double its number. 10% flat over 12 months ≈ 17.97% reducing balance. The quick conversion: multiply the flat rate by 2n ÷ (n+1), where n is the number of payments.
Always ask: "Is that flat or reducing balance?" If a lender won't say plainly, that itself is the answer.

The same loan, both ways

₦1,000,000 over 12 monthly payments.

At 10% flat: interest is charged on the full ₦1,000,000 for the whole year, regardless of what you repay. So interest = ₦1,000,000 × 10% = ₦100,000. Total repayable = ₦1,100,000, split into 12 payments of ₦91,666.67.

At 10% reducing balance: interest each month is charged only on the outstanding balance, which falls every month. The monthly payment works out to ₦87,915.89, and total interest over the year is ₦54,990.65.

| | 10% flat | 10% reducing balance | |---|---|---| | Monthly payment | ₦91,666.67 | ₦87,915.89 | | Total interest | ₦100,000.00 | ₦54,990.65 | | Total repaid | ₦1,100,000.00 | ₦1,054,990.65 |

Same headline rate. Same amount borrowed. Same term. ₦45,009 difference in interest — the flat-rate version costs 82% more.

So what is 10% flat really?

The honest way to express a flat rate is to ask what reducing-balance rate produces the same monthly payment. For ₦1,000,000 over 12 months at ₦91,666.67 a month, the answer is a monthly rate of about 1.4977% — a nominal 17.97% per year, or 19.53% once you compound it.

So "10% flat" is, in the only terms that let you compare it to anything else, an 18% loan.

There's a rule of thumb that gets you close without a calculator:

Approximate reducing-balance rate ≈ flat rate × 2n ÷ (n + 1)

For 12 monthly payments: 10% × 24/13 = 18.46% — near enough to the exact 17.97% to make the decision. The intuition behind the doubling is simple: over the life of the loan your average outstanding balance is roughly half the original amount, so charging interest on the full amount throughout is roughly twice the true cost.

The effect doesn't fade on longer terms. The same ₦1,000,000 at 10% flat per year over 24 months means ₦200,000 of interest, ₦50,000 a month — an equivalent reducing-balance rate of about 18.16%.

Why flat rates are so common here

Flat-rate quoting is not automatically dishonest. It's genuinely simpler to compute and explain, which matters for lenders doing high volumes of small, short loans without much systems infrastructure — cooperatives, microfinance institutions, asset-finance and salary-advance products, and plenty of digital lenders.

The problem isn't the method, it's the comparison. A flat rate presented next to a bank's reducing-balance APR, with no label on either, is a comparison that reliably misleads — and lenders quoting flat rates are rarely in a hurry to correct the impression.

For context on what a genuinely competitive rate looks like right now: the CBN has held its Monetary Policy Rate at 26.5% since February 2026 (CBN Monetary Policy Decisions). Commercial lending sits above that. So a loan advertised at "10%" should immediately raise a question — either it's a flat rate, or there are fees doing the work the interest rate isn't.

The four questions to ask before signing

Is that flat or reducing balance? Everything else depends on the answer.
What is the total amount I will repay? A single number, in naira, that no quoting convention can disguise. If the lender can't produce it, walk.
What fees are on top? Management fees, insurance, and processing charges deducted upfront are effectively extra interest and don't appear in either rate.
What happens if I repay early? On a flat-rate loan, early repayment often saves you nothing at all — the full term's interest was baked in on day one. On reducing balance, paying early genuinely cuts your interest. This is one of the biggest practical differences between the two and almost never gets mentioned upfront.

That last point is worth sitting with. On a true reducing-balance loan, every extra naira you throw at the principal reduces what you owe forever after. On a flat-rate loan, you may be paying off a fixed total that was decided before you made your first payment.

Compare a flat rate against reducing balance on your own numbers →

Worked examples were computed and independently re-checked for this article; the equivalent reducing-balance rates are solved numerically from the standard amortisation formula. The MPR figure is from the CBN's published Monetary Policy Committee decisions, checked as of August 2026. Individual lenders' rates, fees and early-repayment terms vary — always ask for the total repayable in naira. This article is general information, not financial advice.