How EMI is calculated
An EMI (equated monthly instalment) is the fixed amount you pay every month until a loan is repaid. Banks in India work it out on a reducing balance: each month you pay interest only on the loan that's still outstanding, and the rest of the EMI repays principal.
The formula is EMI = P × r × (1 + r)^n ÷ ((1 + r)^n − 1), where P is the loan amount, r is the monthly interest rate (the yearly rate ÷ 12 ÷ 100) and n is the number of monthly instalments. For example, a home loan of ₹50 lakh at 8.5% a year for 20 years (240 months) has an EMI of about ₹43,391. Over the 20 years you'd repay about ₹1.04 crore, of which around ₹54 lakh is interest.
At the start of a long loan most of each EMI is interest, because the outstanding balance is large. In the first year of that ₹50 lakh loan, about ₹4.2 lakh of the ₹5.2 lakh you pay is interest and only about ₹1 lakh reduces the loan. As the balance falls, the split slowly reverses, which you can see in the repayment schedule.