Mortgage Calculator
This mortgage calculator estimates the monthly principal-and-interest payment on a fixed-rate loan. It also shows the loan amount, the down payment in dollars, the total interest you would pay over the life of the loan, and the total of all payments. Taxes, insurance and fees are not included, so treat the result as a starting point.
How to use the mortgage calculator
- Enter the home price and the down payment as a percentage of that price.
- Enter the annual interest rate and the loan term in years.
- Read the monthly payment, then compare terms (for example 30 years against 15 years) to see the trade-off between payment size and total interest.
Formula
M = L × i ÷ (1 − (1 + i)−n), where L is the loan amount, i is the monthly rate (annual rate ÷ 12) and n is the number of monthly payments (years × 12). If the rate is 0, the payment is simply L ÷ n.
Worked examples
30-year loan
A $300,000 home with 20% down gives a $240,000 loan. At 6.5% for 30 years the payment is about $1,516.96 a month. Over 360 payments you pay about $546,107, of which about $306,107 is interest.
15-year loan
The same $240,000 at 6.5% over 15 years costs about $2,090.66 a month, but total interest falls to about $136,318. The payment is about $574 higher, but you save roughly $170,000 in interest.
What drives your monthly payment
Three inputs control a fixed-rate mortgage payment: the amount you borrow, the interest rate and the length of the loan. Small changes in each have large effects over decades.
How amortization works
Your payment stays the same, but its makeup changes. In the first month most of it pays interest; over time more goes to principal. On the $240,000 loan at 6.5% for 30 years, the first payment of $1,516.96 includes about $1,300 of interest and only about $217 of principal. In the last years the balance is almost all principal.
Term and rate: what changes
| $240,000 loan | Monthly payment | Total interest |
|---|---|---|
| 30 years at 6.5% | $1,516.96 | $306,107 |
| 15 years at 6.5% | $2,090.66 | $136,318 |
Costs this calculator does not include
- Property tax and homeowners insurance, often paid monthly through an escrow account.
- Private mortgage insurance (PMI) when the down payment is below 20%.
- HOA dues, maintenance and closing costs.
Ways to reduce total interest
Make extra principal payments, choose a shorter term, make a larger down payment or shop lenders for a lower rate. Even 0.25% off the rate can save thousands over the life of a loan. Always confirm details with a licensed lender.
Practice problems
Try these yourself first, then check your answer. The answers come from the calculator above.
- A $450,000 home, 10% down, 7% rate, 30 years. What is the monthly principal and interest?
Show answer
Monthly payment (principal + interest): $2,694.48
- Same home and rate, but a 15-year term.
Show answer
Monthly payment (principal + interest): $3,640.25
Common mistakes to avoid
- Ignoring property tax, homeowners insurance, HOA fees and (if your down payment is under 20%) mortgage insurance. These can add hundreds per month.
- Comparing loans by monthly payment alone. A longer term lowers the payment but raises total interest.
- Assuming the rate is fixed. Adjustable-rate loans can change the payment later.
Frequently asked questions
How is a monthly mortgage payment calculated?
With the amortization formula shown above. Each payment covers that month’s interest first and the rest reduces the principal, so early payments are mostly interest.
Does this include taxes and insurance?
No. It covers principal and interest only. Add your local property tax, insurance and any HOA dues for a full monthly cost.
Is a 15-year or 30-year mortgage better?
A 15-year loan has a higher payment but much lower total interest. A 30-year loan has a lower payment and more flexibility. The right choice depends on your budget.
How much should I put down?
Many lenders ask for up to 20% to avoid mortgage insurance, but smaller down payments are common. Talk to a lender about your options.
Reviewed September 26, 2026 by the SolveCalcPro editorial team. Found a mistake? Tell us; see our editorial policy.