Every month, your bank deducts a fixed amount from your account. That amount — your Equated Monthly Instalment (EMI) — is not arbitrary. It is the result of a precise mathematical formula that every scheduled bank and NBFC in India is required to use. Understanding it puts you firmly in control of your borrowing decisions.
The Reducing Balance Formula
All home, car, and personal loans in India use the reducing balance method, where interest is charged only on the outstanding principal after each repayment. The standard EMI formula is:
where P = Principal, r = monthly interest rate, n = number of monthly instalments
The monthly interest rate r = annual rate ÷ 12. So for an annual rate of 9%, r = 9/12/100 = 0.0075.
Worked Example
Suppose you borrow ₹30 lakh at 9% per annum for 20 years (240 months).
- P = 30,00,000
- r = 0.09 ÷ 12 = 0.0075
- n = 240
= ₹26,992 per month (approx.)
Over 20 years you pay 240 × ₹26,992 = ₹64.78 lakh total — meaning ₹34.78 lakh is interest on a ₹30 lakh loan. This is why tenure matters enormously.
Why the First Few EMIs Are Mostly Interest
In Month 1, your interest component = ₹30,00,000 × 0.0075 = ₹22,500. So only ₹4,492 reduces your principal. By Month 100, your outstanding is roughly ₹22 lakh, so interest falls to ≈₹16,500 — and principal repayment accelerates. This is called the amortisation schedule.
Key insight: Paying one extra EMI per year from the very start can cut a 20-year loan to roughly 17 years and save you several lakh in interest.
Impact of Tenure on Total Interest
For the same ₹30 lakh at 9%, here's how tenure changes your total outgo:
- 10 years: EMI ₹38,002 · Total ₹45.6 lakh · Interest ₹15.6 lakh
- 15 years: EMI ₹30,428 · Total ₹54.77 lakh · Interest ₹24.77 lakh
- 20 years: EMI ₹26,992 · Total ₹64.78 lakh · Interest ₹34.78 lakh
The 20-year option saves ₹11,000/month vs the 10-year option — but costs you ₹19 lakh extra in interest. The right tenure depends on your income and cash-flow needs.
What the Formula Does Not Tell You
The EMI formula assumes a constant interest rate. On floating-rate loans, your rate resets with every RBI policy change, which can change your EMI or your remaining tenure. Always ask your lender: "If rates rise 1%, will my EMI increase or my tenure extend?"
Verify It Yourself
You never have to take your bank's word for it. Use the EMI calculator on this site to verify any loan your lender quotes — enter the principal, rate, and tenure to get the exact EMI and a full breakdown of interest vs. principal.