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How Reducing-Balance Interest Works (and Why It Saves You Money)

The same 5% rate can cost very different amounts depending on how it's calculated. Here's the difference.

31 July 2026 · 6 min read

"5% per month" sounds like one number, but how that 5% gets applied changes what you actually pay. There are two common approaches, and they're not the same thing.

Flat rate vs. reducing balance

A flat rate charges interest on the full original loan amount for every single instalment, even after you've paid a chunk of it back. A reducing balance — what we use — charges interest only on what you still owe. As your balance goes down, the interest portion of your payment goes down with it.

Key takeaway

Same 5% rate, same loan amount, same term — a flat rate can end up costing meaningfully more in total interest than reducing balance, because it never lets your interest bill shrink as you repay.

A worked example

Borrow RWF 1,000,000 over 4 months at 5% per month on the reducing balance:

PrincipalMonthly paymentTotal interestTotal repayment
RWF 1,000,000RWF 282,012RWF 128,047RWF 1,128,047

Notice the monthly payment stays identical every month — but underneath, the mix changes. Here's the actual breakdown:

InstalmentInterest portionPrincipal portionBalance after
#1RWF 50,000RWF 232,012RWF 767,988
#2RWF 38,399RWF 243,613RWF 524,375
#3RWF 26,219RWF 255,793RWF 268,582
#4RWF 13,429RWF 268,582RWF 0

The interest portion shrinks every month — from RWF 50,000 in month 1 down to just RWF 13,429 in the final month — because there's simply less principal left to charge interest on.

Why this matters to you

It means paying extra toward your loan early, where possible, has a real, immediate effect: less outstanding balance means less interest charged on every instalment after that. It also means there's no benefit to us in dragging out your loan artificially — the math rewards you for repaying, which is the entire point of choosing reducing balance in the first place.

Want to try your own numbers? Use the loan calculator on our Loans page to see your monthly payment and full schedule before you apply.

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