⚖️ Flat vs. Reducing Balance Rate Calculator

How the Flat vs. Reducing Balance Rate Calculator Works

Loans are quoted in two very different ways. With a flat rate, interest is charged on the full original loan amount for the whole term, even though you repay part of it every month. With a reducing balance (declining balance) rate, interest is charged only on the amount you still owe, so it shrinks as you repay. Flat rates are common for car loans, personal loans, and microfinance in many countries, and they look cheaper than they are.

Enter a loan amount, a rate, and a term. The calculator shows the monthly installment and total interest under both methods at the same headline rate, and — most importantly — the effective reducing-balance rate that a flat-rate loan really costs. A flat rate is typically equivalent to a reducing rate of nearly double, which is why comparing loans on the same basis matters.

Formula

Flat:     total interest = P × r × years          installment = (P + total interest) ÷ n
Reducing: installment = P × i × (1 + i)^n ÷ ((1 + i)^n − 1),   i = r ÷ 12
Effective rate of a flat loan = the reducing rate whose installment equals the flat installment
(solved numerically)
P = loan amount, r = annual rate, n = number of monthly installments

How to Use It

1. Enter the loan amount.
2. Enter the annual interest rate as quoted.
3. Enter the term in months.
4. Compare installments and total interest, and read the effective rate of the flat-rate offer.

Frequently Asked Questions

What is the difference between a flat rate and a reducing balance rate?

A flat rate charges interest on the original loan amount for the entire term, while a reducing balance rate charges interest only on the outstanding balance. At the same quoted rate, a flat-rate loan costs considerably more.

How do I convert a flat rate to an effective rate?

Find the reducing-balance rate that produces the same monthly installment. There is no simple exact formula, so this calculator solves it numerically. As a rough rule, the effective rate is close to 1.8–1.9 times the flat rate for typical terms.

Which is better for a borrower?

For the same quoted rate, a reducing-balance loan is always cheaper. To compare offers fairly, compare their effective rates or APRs rather than headline rates, and check fees too.

Related Calculators

• 💳 Loan Calculator (EMI) — Works for any loan type — find your monthly payment and total interest.
• 📅 Amortization Schedule Calculator — See your full year-by-year loan breakdown and what an extra payment saves.
• 💹 Simple Interest Calculator — Interest and total amount for any principal, rate, and time — any currency.
• 🚙 Car Affordability Calculator — Find the car price that fits your budget without financial strain.

Formula and content last reviewed: September 2026. All calculations run in your browser — nothing you enter is sent to or stored on our servers.