How EMI Is Calculated: Reducing Balance vs Flat Rate

An EMI, or equated monthly instalment, is the fixed amount you pay every month until a loan is repaid. The word equated matters: the instalment stays the same, but what is inside it changes every month. In the first month most of it is interest; in the last month almost all of it is principal. Once you see why, two things become clear: why prepaying early saves so much, and why a “flat rate” quoted by a dealer or an app is a very different animal from the rate a bank quotes.

Every figure below is produced by the same function that runs our EMI calculator, so you can reproduce each one by typing the inputs into the tool.

The reducing-balance method (what banks use)

Banks and most NBFCs charge interest only on the outstanding balance, the part of the loan you still owe. Each month, interest is worked out on that balance, the rest of your EMI goes to reduce it, and next month’s interest is worked out on the smaller balance. That is the reducing-balance (or diminishing-balance) method, and it is what the standard EMI formula assumes:

EMI = P × r × (1 + r)^n ÷ ((1 + r)^n − 1)

P = loan amount, n = tenure in months
r = monthly rate = annual rate ÷ 12 ÷ 100

The formula looks dense but it answers one question: what fixed payment, made n times, exactly clears a balance of P when interest accrues at r per month on whatever is left?

Worked example: ₹5,00,000 at 10% for 5 years

• Monthly rate r = 10 ÷ 12 ÷ 100 = 0.008333
• n = 60 months
• EMI = ₹10,623.52
• Total paid over 60 months = ₹6,37,411.20
• Total interest = ₹1,37,411.20

Now look inside the first and the last instalment:

In month 1, interest is simply ₹5,00,000 × 0.008333 = ₹4,166.67; the remaining ₹6,456.85 of the EMI reduces the balance. By month 60 the balance is tiny, so the interest is only ₹87.80. Year by year the picture looks like this:

| 1 | ₹81,134.04 | ₹46,348.20 | ₹4,18,865.96 | | 2 | ₹89,629.81 | ₹37,852.43 | ₹3,29,236.15 | | 3 | ₹99,015.23 | ₹28,467.01 | ₹2,30,220.92 | | 4 | ₹1,09,383.44 | ₹18,098.80 | ₹1,20,837.48 | | 5 | ₹1,20,837.48 | ₹6,644.94 | ₹0.00 |

Year 1 costs ₹46,348.20 in interest; year 5 costs ₹6,644.94. That front-loading is not a trick: it is simply the consequence of owing more at the start. It is also why the prepayment guide says the early years are when a lump sum saves the most.

The flat-rate method (what some dealers and apps quote)

A flat rate charges interest on the original loan amount for the entire tenure, as if you never repaid anything. The arithmetic is deliberately simple:

Total interest = P × flat rate × years
EMI = (P + total interest) ÷ n

Same loan, ₹5,00,000 at a “10% flat” rate for 5 years:

• Total interest = ₹5,00,000 × 10% × 5 = ₹2,50,000
• EMI = (₹5,00,000 + ₹2,50,000) ÷ 60 = ₹12,500

Compare that with the reducing-balance figures above: ₹2,50,000 of interest against ₹1,37,411.20, an EMI of ₹12,500 against ₹10,623.52. Both offers are called “10%”, but one costs ₹1,12,588.80 more.

What a flat rate really equals

The honest way to compare the two is to ask: what reducing-balance rate gives the same EMI as the flat offer? Our calculator’s flatToReducingRate function solves exactly that. For 10% flat over 5 years the answer is 17.27% reducing. Check it: ₹5,00,000 at 17.27% for 60 months gives an EMI of ₹12,498.99, within a rupee of the flat EMI of ₹12,500.

The equivalent reducing rate depends on tenure, because the longer the loan, the longer you pay interest on money you have already returned:

| 12 months | 17.97% | | 24 months | 18.16% | | 36 months | 17.92% | | 48 months | 17.6% | | 60 months | 17.27% | | 84 months | 16.66% |

A rough rule of thumb: a flat rate is close to 1.7 to 1.9 times the equivalent reducing rate for loans of two to five years. Two-wheeler loans, consumer-durable EMIs and some gold or personal loans from small lenders are the usual places you meet flat rates. A bank home loan is always reducing balance.

How to compare two loan offers correctly

1. Ask which method is used. If the quote says “flat”, convert it: type the loan amount and the flat EMI into our calculator and adjust the rate until the EMI matches, or use the table above as a guide.
2. Compare EMIs for the same tenure. Two offers with the same EMI and tenure cost the same, whatever the headline rate.
3. Compare total interest, which the calculator shows directly. For a ₹50 lakh home loan at 8.5% over 20 years the EMI is ₹43,391.16 and total interest is ₹54,13,878.40, more than the loan itself. That is normal for long tenures, and it is why a small rate difference matters: at 20 years each 0.25% changes the total by tens of thousands of rupees.
4. Add the fees. Processing fee, insurance pushed with the loan and prepayment charges (where still allowed) all raise the effective cost. The Key Facts Statement your lender must give you shows the annual percentage rate including such charges.
5. Check the prepayment terms. Under the RBI (Pre-payment Charges on Loans) Directions, 2025, no prepayment charge can be levied on a floating-rate loan taken by an individual for a non-business purpose if the loan was sanctioned or renewed on or after 1 January 2026. For other loans, any charge must be disclosed in the sanction letter, loan agreement and Key Facts Statement.

Common mistakes

• Multiplying the rate by the years. “10% for 5 years means 50% interest” is only true for a flat loan. On a reducing-balance loan the actual interest is ₹1,37,411.20 on ₹5,00,000, about 27.5%.
• Assuming the EMI splits evenly. It never does. Half of a 20-year home loan’s principal is typically repaid only in the last seven or eight years.
• Comparing EMIs across different tenures. A lower EMI over a longer tenure usually means more total interest. Compare total interest, not just the monthly figure.
• Ignoring rounding. Banks round the EMI to the rupee and adjust the final instalment; our calculator rounds to the paisa and absorbs the difference in the last month, which is why the last row of a schedule can differ by a few rupees from the EMI.
• Treating the rate as fixed. Most home loans are floating. When the rate changes, banks usually keep the EMI and change the tenure, so the number of instalments quietly grows. Re-run the calculator after each reset.

Frequently asked questions

Is a reducing-balance loan always cheaper than a flat-rate loan with the same number? Yes. For the same stated percentage, the flat method charges interest on money you have already repaid, so it always costs more. Compare the equivalent reducing rate, or simply the EMI and total interest.

Why does my first EMI have so much interest? Because the balance is largest in month 1. Interest is the balance times the monthly rate, so it falls every month as the balance falls.

Does paying the EMI early in the month reduce interest? Not on a standard loan: interest is calculated on the balance for the month at the agreed rate, not daily. Prepaying extra principal does reduce interest.

Can I convert my flat-rate loan to reducing balance? Only by closing it and taking a new loan. Before you do, check the closure charges in your agreement and compare the total cost of continuing versus refinancing.