How EMI is Calculated: Formula, Steps & Example

If you have ever wondered how a bank turns a loan amount, an interest rate, and a tenure into one neat monthly figure, the answer is a single equation. Indian lenders use the reducing-balance method, where interest is charged only on the amount you still owe. This guide walks through that formula, defines every term, and works a complete example you can reproduce yourself.

The reducing-balance EMI formula

The standard formula is:

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

Each variable means something specific:

• P — Principal. The loan amount you actually borrow, e.g. ₹10,00,000.
• r — Monthly interest rate. The annual rate converted to a monthly decimal: r = annual rate ÷ 12 ÷ 100. So 8.5% per year becomes 8.5 ÷ 12 ÷ 100 = 0.00708333.
• n — Tenure in months. A 20-year loan is 20 × 12 = 240 months.

The two things people most often get wrong are using the annual rate instead of the monthly rate, and entering the tenure in years instead of months. Convert both first and the rest is arithmetic.

A worked example, step by step

Let’s calculate the EMI for a ₹10,00,000 home loan at 8.5% per year for 20 years (240 months).

Step 1 — Find the monthly rate (r). r = 8.5 ÷ 12 ÷ 100 = 0.00708333

Step 2 — Compute (1 + r)ⁿ. (1 + 0.00708333)²⁴⁰ = (1.00708333)²⁴⁰ ≈ 5.4517

Step 3 — Plug into the formula. Numerator: P × r × (1 + r)ⁿ = 10,00,000 × 0.00708333 × 5.4517 ≈ 38,616 Denominator: (1 + r)ⁿ − 1 = 5.4517 − 1 = 4.4517

Step 4 — Divide. EMI = 38,616 ÷ 4.4517 ≈ ₹8,678

So the monthly EMI is about ₹8,678. Over 240 months you pay 8,678 × 240 = ₹20,82,720 in total, of which ₹10,00,000 is your principal and roughly ₹10,82,776 is interest. You borrowed ten lakh and repaid almost twenty-one lakh — a vivid illustration of how interest adds up over a long tenure. You can verify these exact numbers in our EMI Calculator.

How the amortization schedule works

The EMI is fixed, but the way each payment is split between interest and principal changes every single month. That month-by-month breakdown is the amortization schedule, and it is built like this:

1. Interest for the month = outstanding balance × monthly rate (r).
2. Principal for the month = EMI − that interest.
3. New balance = old balance − that principal.
4. Repeat for the next month using the new, lower balance.

For our example, the very first month looks like:

Notice that in month one, over 80% of your EMI is interest and barely ₹1,595 reduces the loan. As the balance shrinks, the interest slice falls and the principal slice grows, until in the final months almost the entire EMI repays principal. This front-loading of interest is exactly why early prepayments are so powerful.

Reducing balance vs flat interest

Not every “interest rate” is calculated the same way, and the difference matters a lot:

• Reducing balance: interest is charged only on the outstanding balance, which keeps falling. This is what the formula above uses and what genuine home and most personal loans follow.
• Flat rate: interest is charged on the full original principal for the entire tenure, regardless of how much you have repaid. A flat rate always costs more than a reducing rate of the same number — a “12% flat” loan can have an effective reducing rate closer to 21–22%.

If a lender quotes a flat rate, ask for the effective (reducing-balance) rate or the APR so you can compare loans fairly. Two loans with the same headline percentage can have very different true costs.

How prepayment changes the maths

A prepayment is any amount you pay over and above your scheduled EMI, and it goes straight toward reducing the principal. Because interest is calculated on the outstanding balance, knocking down the principal early cuts every future interest charge.

You generally have two choices when you prepay:

• Reduce the tenure (keep the EMI the same) — this saves the most interest and gets you debt-free sooner.
• Reduce the EMI (keep the tenure the same) — this eases monthly cash flow but saves less.

Reducing the tenure is almost always the cheaper option overall. As a rule of thumb, prepayments made in the early years — when the interest slice is largest — deliver far more savings than the same amount paid near the end.

A note on accuracy: RBI guidelines bar lenders from charging prepayment penalties on floating-rate loans taken by individuals, but fixed-rate loans and some business loans may still attract charges. Confirm the terms with your lender before prepaying.

Try it on your own numbers

Doing this by hand once is worth it for the intuition, but you don’t have to repeat it. Enter your figures into the EMI Calculator to get an instant EMI and a full amortization table, or use the Home Loan EMI Calculator for a housing loan with prepayment options. If you want the plain-English version of what an EMI is before diving into the maths, start with our guide on what EMI is.