How EMI Is Calculated, Step by Step
⏱ 2 min readYour EMI (Equated Monthly Instalment) looks like one flat number, but inside it the mix of interest and principal changes every month. Here is the exact formula banks use, a worked example, and the levers that move it.
The formula
EMI = P × r × (1 + r)^n ÷ ((1 + r)^n − 1), where P is the loan amount, r is the monthly interest rate (annual rate ÷ 12 ÷ 100) and n is the number of monthly instalments.
This is the reducing-balance method: each month's interest is charged only on the principal still outstanding, which is why the same EMI slowly shifts from interest-heavy to principal-heavy.
Worked example: ₹30 lakh home loan
Take ₹30,00,000 at 8.5% per annum for 20 years (240 months). The monthly rate is 8.5 ÷ 12 ÷ 100 = 0.7083%.
- EMI ≈ ₹26,035 per month
- Total paid over 20 years ≈ ₹62.5 lakh
- Total interest ≈ ₹32.5 lakh — more than the loan itself, which is normal at long tenures
Why early EMIs barely reduce your loan
In month one of the example, interest is 0.7083% of ₹30 lakh ≈ ₹21,250 — so only about ₹4,785 of the ₹26,035 EMI actually repays principal. Twenty years later the proportions are reversed. This is also why prepaying in the early years saves dramatically more interest than prepaying late.
What moves your EMI
Three inputs decide everything:
- Principal — EMI scales directly: borrow 10% less, pay 10% lower EMI.
- Rate — on the example loan, 8.5% → 8.0% drops the EMI from about ₹26,035 to about ₹25,093 and saves roughly ₹2.3 lakh of interest.
- Tenure — stretching the tenure lowers the EMI but raises total interest sharply; shortening does the reverse.
Frequently asked questions
Does my EMI change when interest rates change?
On a floating-rate loan, yes — though many banks keep the EMI fixed and stretch the tenure instead, unless you ask them to re-fix the EMI.
Is the EMI the same every month?
On a fixed-rate loan, yes. What changes invisibly is the split inside it: early EMIs are mostly interest, later EMIs mostly principal.
What is reducing-balance interest?
Interest charged each month only on the principal still outstanding, rather than on the original loan amount. Home, car and most bank loans in India use this method.