In this guide
This guide explains the building blocks of a mortgage — principal, interest and term — how the monthly payment is worked out, how amortization shifts each payment from interest to principal, and how to estimate total interest with the Mortgage Calculator.
- What a mortgage is
- Principal, interest and loan term
- How the monthly EMI is calculated
- Amortization and total interest
- A checked illustrative example
What a mortgage is
A mortgage is a secured loan for buying a home or other property. The lender pays most of the purchase price, you pay the rest as a down payment, and the property acts as security until the loan is repaid. In India the same arrangement is usually called a home loan.
Exact terms — eligibility, fees, the interest-rate type, prepayment rules and what happens on default — depend on the lender, the country and the loan agreement, so always read the specific offer.
Principal, interest and loan term
These three numbers decide your monthly payment and the total interest you pay over the life of the loan. A longer term lowers the monthly payment but usually raises the total interest considerably.
- Principal: the amount you borrow — the property price minus your down payment.
- Interest rate: the yearly cost of borrowing, charged on the balance still outstanding.
- Loan term (tenure): how long you take to repay, often expressed in years.
How the monthly EMI is calculated
For a fixed-rate loan repaid in equal monthly instalments, EMI = P × r × (1 + r)^n ÷ ((1 + r)^n − 1), where P is the principal, r is the monthly interest rate (annual rate ÷ 12 ÷ 100) and n is the number of monthly payments.
This payment stays the same each month, but what it is made of changes. Property taxes, insurance and fees are not part of this formula, so a real monthly housing cost can be higher.
Amortization: where each payment goes
Each month, interest is charged on the outstanding balance and the rest of the EMI reduces the principal. Early on the balance is large, so interest takes most of the payment. As the balance falls, interest shrinks and more of each payment goes to principal. This gradual repayment schedule is called amortization.
A year-by-year amortization table shows how much principal and interest you pay each year and the balance left — the Mortgage Calculator builds one automatically.
Illustrative example
Hypothetical example, in no particular currency: a property costs 400,000 and the down payment is 80,000, so the loan is 320,000. At an assumed 6.5% a year for 30 years, the monthly rate is about 0.5417% and there are 360 payments.
The monthly payment works out to about 2,022.62. Over 360 payments you pay about 728,142 in total, of which about 408,142 is interest — more than the amount borrowed. In the very first month, about 1,733.33 is interest and only about 289.28 reduces the principal; after the first year the balance is still about 316,423.
Shortening the same loan to 15 years raises the payment to about 2,787.54 a month, but total interest falls to about 181,758. The rate used here is an example only, not a current market rate.
| Term | Monthly payment | Total paid | Total interest |
|---|---|---|---|
| 30 years | ≈ 2,022.62 | ≈ 728,142 | ≈ 408,142 |
| 15 years | ≈ 2,787.54 | ≈ 501,758 | ≈ 181,758 |
How the calculators help
The Mortgage Calculator works in any currency and starts from property price and down payment, which suits buyers anywhere. For an Indian home loan in rupees, the Home Loan Calculator gives the same EMI maths with Indian formatting, and the EMI Calculator handles any loan amount directly.
Estimates assume a fixed rate for the whole term. If your rate is floating or you plan to prepay, actual figures will differ — see our guides on fixed vs floating rates and EMI vs prepayment.
Common mistakes
A few minutes comparing scenarios can reveal large differences in total cost.
- Looking only at the monthly payment and ignoring total interest over the term.
- Forgetting taxes, insurance, maintenance and fees that sit outside the EMI.
- Using the annual rate in the formula without dividing by 12.
- Assuming a floating rate will stay where it is today.
- Choosing the longest term by default without comparing a shorter one.
Conclusion
A mortgage spreads the cost of a property over many years through equal monthly payments. Understanding principal, rate, term and amortization makes it easier to compare offers — run your own scenarios and confirm the final terms with your lender.