How EMI Is Actually Calculated (With a Worked Example)

An EMI (equated monthly installment) is one fixed number, but it's quietly doing two different jobs every month: paying interest on what you still owe, and chipping away at the principal itself. The formula that produces that fixed number is worth understanding, because it explains a few things about loans that otherwise seem confusing.

The formula

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

Where:

• P is the principal (the amount you're borrowing)
• r is the monthly interest rate (annual rate ÷ 12 ÷ 100)
• n is the total number of monthly payments (loan term in years × 12)

That's it, three inputs. Everything an EMI calculator does is plug numbers into that formula and, usually, break the result down month by month afterward.

A worked example

Say you borrow ₹10,00,000 at 9% annual interest over 5 years.

• P = 1,000,000
• r = 9 ÷ 12 ÷ 100 = 0.0075 (0.75% per month)
• n = 5 × 12 = 60 months

Working through the formula: (1 + 0.0075)⁶⁰ ≈ 1.5658. Plugging that back in:

EMI = 1,000,000 × 0.0075 × 1.5658 / (1.5658 − 1)
    = 11,743 / 0.5658
    ≈ ₹20,756 per month

Over 60 months that's a total of roughly ₹12,45,360 paid, against a ₹10,00,000 loan, meaning about ₹2,45,360 goes to interest over the life of the loan. EMI Calculator does this same calculation instantly for any amount, rate, and term, and shows the principal-versus-interest split so you're not just staring at one final number.

Why the interest portion shrinks every month

This is the part that trips people up: the EMI itself is fixed, but what it's made of changes every single month.

In month one, interest is calculated on the full ₹10,00,000 you still owe: 0.75% of that is ₹7,500. The rest of your ₹20,756 payment, about ₹13,256, goes toward principal. In month two, you owe slightly less (₹10,00,000 minus that ₹13,256), so 0.75% of a slightly smaller number produces a slightly smaller interest charge, and slightly more of your fixed payment goes to principal instead. Repeat that sixty times and, by the final month, almost the entire payment is principal with barely any interest left to charge.

This is also why paying even a small amount extra early in a loan matters more than the same extra amount paid later: extra principal paid down in month one reduces the balance interest gets calculated on for all 59 remaining months, while the same extra payment in month 55 only affects 5 remaining months.

Term length is a real tradeoff, not just "lower payment good"

Stretching the same ₹10,00,000 loan from 5 years to 10 years at the same 9% rate roughly halves the EMI, which is the appealing part. But you're now paying interest on a shrinking-but-still-substantial balance for twice as long, and the total interest paid over the full term ends up meaningfully higher, not lower. A lower EMI can be the right call if it's the difference between comfortably affording the payment and not, but it's worth actually running both terms through a calculator side by side rather than assuming "lower monthly payment" is free.

Where this fits with the rest of your finances

An EMI calculation only tells you what one loan costs. Two natural follow-ups once you know that number: checking what a SIP of the same monthly amount could have grown into instead, if you're weighing a big purchase against investing that money, and checking how the loan's interest (on a home loan especially) might affect your income tax if you're eligible for interest deductions.

The short version

EMI is a fixed number calculated once, up front, from the loan amount, rate, and term, but the interest-versus-principal split behind that fixed number shifts every month as your outstanding balance shrinks. A longer term lowers the monthly payment but raises total interest paid, and extra payments matter more the earlier in the loan you make them.