This is one of the most common sources of confusion — and occasionally mis-selling — in consumer lending. Two loans advertised at "8%" and "15%" can end up costing almost exactly the same, because they're calculated on completely different bases.
Flat rate: interest on the original amount, always
Under a flat rate, interest is calculated on the full original principal for every single month of the tenure — even in month 59 of a 60-month loan, when you've already repaid most of the principal. The lender simply adds up (principal × rate × years) as total interest, then divides everything evenly into equal installments.
Reducing balance: interest on what you still owe
Under reducing balance (used by virtually all home, car, and personal loans, and by this site's calculators), interest is charged only on the outstanding balance each month. As you repay principal, the balance shrinks, so the interest charged each month shrinks too.
Side-by-side: ₹1,00,000 over 3 years
| Method | Quoted rate | Total interest | Effective reducing-balance rate |
|---|---|---|---|
| Flat rate | 8% flat | ₹24,000 | ≈ 14.5% |
| Reducing balance | 14.5% | ≈ ₹24,000 | 14.5% |
An 8% flat rate loan and a 14.5% reducing-balance loan end up costing almost the same amount. As a rule of thumb, a flat rate roughly doubles to become its equivalent reducing-balance rate (the exact multiplier depends on tenure, but 1.8x-2x is typical).
How to protect yourself
- Always ask explicitly: "Is this rate flat or reducing balance?"
- Ask for the APR or effective annual rate, which is required disclosure in most regulated lending and always reflects the true reducing-balance-equivalent cost.
- Run the loan amount, rate, and tenure through a reducing-balance calculator (like the ones on this site) and compare the resulting EMI to what the lender quoted — a big mismatch usually means you're looking at a flat rate.