How EMI Is Actually Calculated (With the Full Formula)

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Every loan brochure shows you a monthly EMI number, but almost none of them show you how that number is actually produced. Once you see the formula, EMI stops feeling like a black box and starts feeling like ordinary arithmetic.

The formula

EMI is calculated as:

EMI = P × r × (1 + r)^N ÷ ((1 + r)^N − 1)

Three inputs feed this formula. P is the principal — the amount you're actually borrowing. r is the monthly interest rate, found by taking the annual rate, dividing by 12, and dividing by 100 to convert it to a decimal. N is the number of monthly installments, i.e. your tenure in months.

Why the EMI stays flat but the loan doesn't feel flat

Here's the part most people miss: even though you pay the same EMI every single month, the mix of principal and interest inside that payment changes constantly. In the early months, most of your EMI is interest, and only a small sliver chips away at the principal. By the final year of the loan, that flips — most of the payment is principal, and very little is interest.

This is simply because interest is charged on the *outstanding* balance each month. Early on, the outstanding balance is large, so the interest portion is large. As the balance shrinks, so does the interest charged on it, leaving more of the fixed EMI to go toward principal.

A worked example

Take a ₹10,00,000 loan at 9% annual interest over 60 months (5 years).

First, convert the annual rate to a monthly decimal rate: 9 ÷ 12 ÷ 100 = 0.0075.

Plug P = 1,000,000, r = 0.0075, N = 60 into the formula, and the EMI comes out to roughly ₹20,758 per month.

Over 60 months, that's a total payment of about ₹12,45,000 — meaning roughly ₹2,45,000 of the total is interest, even though the loan is only ₹10,00,000.

What happens with a 0% interest loan

If r is 0 (an interest-free loan or promotional financing), the formula above breaks down mathematically (dividing by zero), so it's handled as a special case: EMI simply becomes the principal divided by the number of months, since there's no interest to add.