A bank quotes you an interest rate and an EMI, and that is usually where the thinking stops. We ran the numbers on a typical home loan month by month to see where the money actually goes and which choices change the total. Three results surprised us: how little principal you repay in the first years, how much the timing of a prepayment matters, and how far a “flat rate” is from the rate you really pay.
How an EMI is calculated
EMI stands for equated monthly instalment: one fixed payment that, over the loan term, repays the principal and the interest on whatever you still owe. The formula is
EMI = P × r × (1 + r)n ÷ ((1 + r)n − 1)
where P is the loan amount, r is the monthly rate (annual rate ÷ 12 ÷ 100) and n is the number of monthly payments. Worked example: ₹10 lakh at 9% for 5 years. Here r = 0.0075 and n = 60, which gives an EMI of ₹20,758. You pay ₹20,758 × 60 = ₹12,45,502 in total, so the interest is ₹2,45,502. Banks round to the rupee and may differ by a few rupees from this figure.
Interest is charged each month on the outstanding balance. That is what “reducing balance” means, and it is how almost every home, car and personal loan is priced. Every figure below assumes monthly reducing balance, payments at month end, a fixed rate for the whole term, and no fees.
What a ₹25 lakh loan costs at different rates and tenures
| Tenure | 8.5% | 9.5% | 10.5% |
|---|---|---|---|
| 10 years | ₹30,996 · interest ₹12.2 L | ₹32,349 · ₹13.8 L | ₹33,734 · ₹15.5 L |
| 15 years | ₹24,618 · ₹19.3 L | ₹26,106 · ₹22.0 L | ₹27,635 · ₹24.7 L |
| 20 years | ₹21,696 · ₹27.1 L | ₹23,303 · ₹30.9 L | ₹24,959 · ₹34.9 L |
| 25 years | ₹20,131 · ₹35.4 L | ₹21,842 · ₹40.5 L | ₹23,605 · ₹45.8 L |
Read across the 8.5% column. Stretching from 10 to 25 years lowers the EMI by about a third (₹30,996 to ₹20,131) but nearly triples the interest, from ₹12.2 lakh to ₹35.4 lakh. At 25 years the interest alone is 142% of the amount you borrowed.
What one percentage point and five extra years cost
On a ₹50 lakh, 20-year loan, a single point of interest is a lot of money:
| Rate | EMI | Total interest | Extra interest vs 8.5% |
|---|---|---|---|
| 8.5% | ₹43,391 | ₹54.1 lakh | – |
| 9.5% | ₹46,607 | ₹61.9 lakh | ₹7.7 lakh |
| 10.5% | ₹49,919 | ₹69.8 lakh | ₹15.7 lakh |
Each extra point adds about ₹3,200 to the monthly EMI and roughly ₹7.7 to ₹8 lakh to the total. That is why a quarter point from negotiation or a lender switch is worth chasing. Tenure works the other way, tempting you with a smaller EMI. Here is ₹50 lakh at 9%:
| Tenure | EMI | Total interest |
|---|---|---|
| 15 years | ₹50,713 | ₹41.3 lakh |
| 20 years | ₹44,986 | ₹58.0 lakh |
| 25 years | ₹41,960 | ₹75.9 lakh |
| 30 years | ₹40,231 | ₹94.8 lakh |
Going from 15 to 20 years lowers the EMI by 11% but raises the total interest by 40%. Going from 20 to 30 years lowers the EMI by another 11% and raises the interest by a further 64%. The first few years of extra tenure buy the most relief per rupee of interest; after that you pay a lot for very little.
Where your EMI goes: the front-loading effect
Because interest is charged on the balance, and the balance is highest at the start, the early EMIs are mostly interest. This is the month-by-month split for ₹50 lakh at 9% over 20 years (EMI ₹44,986):
| Month | Interest | Principal | Interest share of EMI | Loan repaid so far |
|---|---|---|---|---|
| 1 | ₹37,500 | ₹7,486 | 83% | 0.1% |
| 12 | ₹36,859 | ₹8,128 | 82% | 1.9% |
| 60 | ₹33,352 | ₹11,634 | 74% | 11.3% |
| 120 | ₹26,771 | ₹18,215 | 60% | 29.0% |
| 180 | ₹16,467 | ₹28,519 | 37% | 56.7% |
| 228 | ₹4,164 | ₹40,822 | 9% | 89.7% |
In the first year you pay ₹4,46,200 in interest and shrink the loan by only about ₹93,600. After 10 years, half the term, you have repaid 29% of the principal. This is also why selling or switching lenders early feels so unrewarding: you have paid a lot and still owe most of it.
Prepayment: when you pay matters more than how much
We tested prepayments on the same ₹50 lakh, 9%, 20-year loan, which costs ₹58.0 lakh in interest if you pay nothing extra. Each lump sum is ₹5 lakh and keeps the EMI unchanged, so the loan ends sooner.
| What you do | Loan ends after | Interest saved |
|---|---|---|
| Nothing | 20 years | – |
| Add ₹2,000 every month | 17.9 years | ₹7.4 lakh |
| Add ₹5,000 every month | 15.5 years | ₹15.2 lakh |
| Add ₹10,000 every month | 12.8 years | ₹23.7 lakh |
| ₹5 lakh once, in month 12 | 15.8 years | ₹17.7 lakh |
| ₹5 lakh once, in month 60 | 16.9 years | ₹11.7 lakh |
| ₹5 lakh once, in month 120 | 18.0 years | ₹6.2 lakh |
| ₹5 lakh once, in month 180 | 18.7 years | ₹2.4 lakh |
The same ₹5 lakh saves seven times more in month 12 than in month 180, because it removes interest for many more years. Small regular prepayments also add up: ₹5,000 extra a month finishes the loan 4.5 years early and saves ₹15.2 lakh.
Flat rate vs reducing-balance rate
Some personal, two-wheeler and consumer loans quote a flat rate, where interest is charged on the original amount for the whole term. You keep paying down the balance, so the real cost is much higher. We converted flat rates into the reducing-balance rate that gives the identical EMI:
| Flat rate | 1 year | 3 years | 5 years |
|---|---|---|---|
| 6% | 10.9% | 11.1% | 10.9% |
| 8% | 14.5% | 14.6% | 14.1% |
| 10% | 18.0% | 17.9% | 17.3% |
| 12% | 21.5% | 21.2% | 20.3% |
As a rule of thumb, multiply a flat rate by about 1.8 to compare it with a bank's reducing-balance rate. “8% flat” is a 14%-plus loan. Always ask for the reducing-balance rate or the total amount payable, and compare lenders on that.
What these numbers do not include
- Processing fees, insurance and charges. They raise the real cost and are not in the EMI formula. Ask for the all-in cost.
- Floating rates. Many home loans are floating-rate. If the rate changes, your EMI or tenure changes, so treat the tables as the plan at today's rate.
- Prepayment charges. Rules differ by loan type and lender, and some loans charge for early repayment. Check your agreement before you prepay.
- Bank rounding. Lenders round the EMI and may calculate interest slightly differently. Expect small differences from any calculator.
- This is arithmetic, not advice. It cannot tell you whether prepaying beats investing the same money. Use your own situation and a qualified adviser for that.
Try your own numbers
- Open the EMI Calculator. Its Home Loan and Car Loan modes can start from the price.
- Enter the loan amount, the annual rate and the tenure. The EMI, total interest and payoff date update.
- Open the amortization schedule to see the interest and principal split for every month.
- Type an amount into Extra Monthly Contribution to see how many months and how much interest it saves.
- Compare lenders on the same tenure, and also compare the effect of one point either way using the first two tables above.
Everything runs in your browser, so the loan details you type are not sent anywhere. If you are also weighing what to do with spare money, our compound interest guide shows what the same amount can grow to, and the mortgage guide covers US-style loans with tax, insurance and PMI.
