Mortgage Calculator

What this mortgage calculator does

Buying a home is the biggest purchase most people ever make, and the headline price tells you almost nothing about what you will actually pay each month. This mortgage calculator turns three simple inputs — the loan amount, the interest rate and the term — into the number that really matters: your monthly principal-and-interest payment. It also shows the total amount repaid over the whole loan and how much of that is pure interest, so you can see the true cost of borrowing before you sign anything.

The tool covers the core of any fixed-rate repayment mortgage. It does not add property taxes, homeowners insurance, HOA dues or private mortgage insurance (PMI), which together make up the "PITI" figure your lender quotes — so treat the result as the loan portion of your payment and add those local costs on top. Because it runs entirely in your browser, nothing you type is stored or sent anywhere.

How to use it, step by step

1. Enter the loan amount. This is the home price minus your down payment — the sum you are actually borrowing, not the sale price.
2. Enter the annual interest rate. Use the rate (APR or note rate) your lender quoted, for example 6.5. You can change it by 0.25 at a time to see how sensitive the payment is.
3. Enter the term in years. Most US mortgages are 30 years; 15-year loans cost more per month but far less in total interest.
4. Read your result. The monthly payment, total repaid and total interest update instantly. Adjust any field to compare scenarios side by side.

The formula explained

The calculator uses the standard amortization formula for a fixed-rate loan:

Each month, interest is charged on the outstanding balance and the rest of your payment reduces the principal. Early on, most of your payment is interest; later, most of it pays down the balance. This shift is called amortization, and it is why paying a little extra in the first years saves so much interest — you knock out balance that would otherwise have accrued interest for decades.

Worked examples

How rate and term move the payment

Principal and interest only. Taxes, insurance, HOA and PMI are extra. Figures rounded.

When to use a mortgage calculator

• Setting a budget before you start house-hunting, so you only view homes you can comfortably afford.
• Comparing offers from different lenders — plug in each rate to see the real monthly difference.
• Deciding between 15- and 30-year terms by weighing a higher payment against huge interest savings.
• Testing extra payments by lowering the loan amount or term to mimic paying down principal faster.
• Refinancing checks — see whether a new, lower rate cuts your payment enough to justify closing costs.

Tips and common mistakes

Don't confuse the loan amount with the home price. The calculator wants what you are borrowing — subtract your down payment first. Don't forget the extras. Property tax and insurance can add hundreds of dollars; lenders escrow these, so your real bill is higher than the P&I shown here. Watch the term, not just the rate. Stretching to 30 years lowers the payment but can double your total interest. And remember that an adjustable-rate mortgage (ARM) only fixes the rate for an introductory period — this tool assumes the rate stays constant, so use it for fixed-rate loans or for the fixed phase of an ARM.