Mortgage payment calculator:
the formula behind your monthly EMI

What your monthly mortgage payment is made of

A mortgage payment is the fixed monthly amount that repays a property loan together with the interest charged on it, so that the balance reaches zero at the end of the term. In India you will see it called an EMI (equated monthly instalment); the arithmetic is identical.

The calculation needs only three inputs: the amount you borrow, the interest rate and the number of monthly payments. Property tax, insurance, society charges and fees are separate and are not part of this formula. Some countries bundle taxes and insurance into the monthly bill; check what your own lender includes.

It also applies to loans against property. Whenever a loan is repaid in equal monthly instalments from a reducing balance, the same formula gives the instalment, whether the loan buys a house, funds a renovation or is raised against an existing property.

Because the payment is fixed while the balance falls, it is a mix: early payments are mostly interest, later ones mostly principal. The loan amortization guide shows that split row by row. This page focuses on how the payment itself is worked out.

The mortgage payment formula

1. 1Divide the annual rate by 12 and write it as a decimal: 9% becomes 0.0075.
2. 2Multiply the number of years by 12 to get n.
3. 3Calculate (1 + r) raised to the power n.
4. 4Substitute into the formula and divide.

The step people get wrong is the power. Most calculators have a power key; in a spreadsheet use ^ or the PMT function with the monthly rate and the number of months.

Worked example: ₹60 lakh at 9% for 25 years

A quick sanity check is to look at the first month. Interest is 60,00,000 × 0.0075 = ₹45,000, so ₹5,352 of the ₹50,352 payment reduces principal. That is only about 11% of the payment, which surprises most first-time borrowers.

Interest is about 1.5 times the amount borrowed in this example. That is not unusual for a 25-year loan at this rate, and it is the most important number to see before signing.

How rate and term change the payment

A one percentage point change in rate moves the payment by roughly ₹4,000 to ₹4,200 here, and total interest by more than ₹12 lakh. On a floating-rate loan this is the risk you carry.

On a fixed-rate loan the payment never changes until the term ends. On a floating-rate loan the lender resets the rate from time to time and either the EMI or the tenure adjusts. Both are legitimate, but with floating you should always model a higher rate before you commit.

Term matters as well. At 9%, the same ₹60 lakh costs about ₹53,984 a month over 20 years and about ₹48,277 over 30 years. The longer loan feels easier but costs far more in interest.

Use this table as a quick estimator: payment per lakh × number of lakhs. For ₹60 lakh at 9% over 25 years, 839 × 60 = ₹50,340, close to the exact figure.

Working backwards: how much can you borrow?

Most buyers start from a budget, not a loan amount. Rearranging the same formula gives the maximum loan for a payment you are comfortable with.

Suppose you can afford ₹40,000 a month at an assumed 9% over 20 years. With r = 0.0075 and n = 240, (1 + r)^−240 is 0.1664, so P = 40,000 × (1 − 0.1664) ÷ 0.0075 ≈ ₹44,45,798. Stretching the same payment to 25 years supports about ₹47,66,465.

Remember that the loan amount is not the property budget: add your down payment and subtract the one-time costs of buying. That gives you a realistic ceiling to take to a property search.

Is the payment affordable?

A common rule of thumb is that all your loan EMIs together should not exceed roughly 40% of your monthly take-home income. Lenders apply their own limits, but the rule is a good personal guardrail.

Working backwards from the example, an EMI of ₹50,352 at a 40% share needs a take-home income of about ₹1,25,880 a month. At 45% the figure would be about ₹1,11,893.

• List your other EMIs, rent and fixed costs before using the rule; the 40% is for all loans combined.
• Check the payment at a rate 1 or 2 percentage points higher than today's.
• Keep an emergency fund separate from your down payment.
• Remember one-time costs: stamp duty, registration, processing fees and furnishing.

Mistakes in mortgage payment calculations

• Plugging the annual rate in as r. The formula needs the monthly rate.
• Mixing years and months. A 25-year loan has n = 300, not 25.
• Using the property price as P. P is the loan amount after your down payment.
• Ignoring processing fees and insurance that are added to or financed with the loan.
• Comparing loans only by EMI. Compare total interest and fees as well.

Another quiet error is comparing offers with different terms. A lender quoting a lower rate on a 30-year loan can still cost you more in total than a slightly higher rate on 20 years. Put the total repayment next to the monthly payment for every option.

Once the loan is running, the formula is the baseline for every later decision. Extra payments, a rate reset or a balance transfer all change the schedule relative to it, which is why the extra mortgage payments guide starts from the same EMI and then shows how much sooner you can finish.

A calculator gives a clean answer, but a lender's sanction letter is final. Dates of first payment, rounding and rate resets can make the actual EMI differ slightly from your estimate, so use the number for planning and confirm it in writing.