How EMI is Calculated — The Reducing Balance Formula Explained

Every loan — home, car, personal, education — comes with an EMI. Equated Monthly Instalment. One fixed number you pay every month until the debt is clear. But behind that single number is a formula that determines how much goes to interest versus principal each month.

The formula

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

Where:

• P = Principal (loan amount)
• r = Monthly interest rate (annual rate ÷ 12 ÷ 100)
• n = Number of months (tenure)

This is the reducing-balance or amortization formula. It guarantees a fixed payment each month while the principal-interest split shifts over time.

Why early payments are mostly interest

In month 1, the outstanding balance is the full loan amount. Interest is charged on that entire balance. So the interest portion of your first EMI is large, and the principal portion is small.

As months pass, the outstanding balance shrinks (because you’ve been paying off principal). Interest is now charged on a smaller amount. So more of your fixed EMI goes toward principal.

By the final months, almost all of your EMI is principal repayment.

Worked example

₹50,00,000 loan at 8.5% for 20 years (240 months):

r = 8.5 / 12 / 100 = 0.007083
(1 + r)ⁿ = (1.007083)^240 = 5.4326
EMI = 50,00,000 × 0.007083 × 5.4326 / (5.4326 − 1)
EMI = ₹43,391

Total payment: ₹43,391 × 240 = ₹1,04,13,840
Total interest: ₹54,13,840 — more than the loan itself!

How to reduce total interest

1. Shorter tenure — Even 2 years less can save lakhs in interest
2. Prepayments — Paying extra reduces the principal faster
3. Lower rate — Refinancing from 9% to 8% on a ₹50L loan saves ~₹5L over 20 years
4. Higher EMI — If your income grows, increase EMI proportionally

When to use an EMI calculator

• Before taking any loan — know your monthly commitment
• Comparing offers from different lenders
• Planning prepayment strategy
• Understanding the true cost (principal + interest)

Try the OurDailyCalc EMI calculator — it shows the amortization schedule and principal-interest split visually.

TL;DR

• EMI uses the reducing-balance formula: fixed payment, shifting principal/interest ratio
• Early payments are interest-heavy; late payments are principal-heavy
• Total interest on a 20-year home loan often exceeds the principal
• Shorter tenure and prepayments are the most powerful ways to save