Reducing balance vs flat-rate EMI — why your bank's number never matches a quick calculator

If you've ever punched a loan amount, rate, and tenure into two different EMI calculators and gotten two different monthly payments, the calculators probably aren't broken — they're using different methods to charge interest. Almost all formal loans in India (home loans, most personal loans, car loans from banks) use the reducing balance method. Some smaller lenders and older-style consumer loans still quote a flat rate. The two produce meaningfully different real costs for what looks like the same headline rate.

Reducing balance: interest on what you still owe

Under reducing balance, interest each month is charged only on the outstanding principal — the amount you haven't paid back yet. As you pay down the loan, the interest portion of each EMI shrinks and the principal portion grows, even though the total EMI stays flat for the life of the loan.

The formula behind our EMI Calculator:

EMI = P × r × (1 + r)^n / ((1 + r)^n − 1)

where P is the loan principal, r is the monthly interest rate (annual rate ÷ 12 ÷ 100), and n is the number of monthly installments.

A ₹5,00,000 loan at 10% annual interest over 5 years (60 months) works out to an EMI of roughly ₹10,624 — and the total interest paid over the loan's life is around ₹1,37,440, not ₹2,50,000 (which is what a naive "10% of 5,00,000 × 5 years" calculation would suggest).

Flat rate: interest on the original amount, every time

Under a flat rate, interest is calculated once on the full original principal and stays fixed for the entire tenure, even though your outstanding balance is dropping every month. The stated "flat rate" therefore has to be lower than the equivalent reducing-balance rate to represent a comparable real cost — and lenders quoting flat rates don't always make that comparison obvious.

Total interest = P × flat rate × tenure (years)
EMI = (P + total interest) / number of months

The same ₹5,00,000 at a 10% flat rate over 5 years gives total interest of ₹2,50,000 — more than 80% higher than the reducing-balance figure at the same headline rate. This is the number that trips people up when comparing offers: a "10% flat" loan is not the same deal as a "10% reducing" loan, even though the paperwork uses the identical word "10%."

What this means when you're comparing two loan offers

If one lender quotes a flat rate and another quotes reducing balance, you cannot compare the two rates directly — you have to convert one into the other's terms, or better, compare the actual EMI and total repayment amount each one produces for your loan size and tenure. As a rough rule of thumb, a flat rate is often close to half the equivalent reducing-balance rate for a similar total cost, but this ratio shifts with tenure length, so it's not reliable enough to use for an actual decision — only for spotting when something needs a closer look.

Why the calculator's number might still differ slightly from your bank's

Two things beyond the formula affect the final figure: processing fees (which some banks fold into the effective rate and others don't), and how the bank rounds the EMI — to the nearest rupee, upward, or by adjusting the final installment. Our calculator shows the pure reducing-balance math; your bank's sanction letter is the source of truth for fees and rounding.

Run your own numbers on the EMI Calculator — it also shows the interest and principal split for every month, not just the final total.