Mortgage Calculator
with Extra Payments

What the monthly estimate includes

Principal pays down the balance you borrowed. Interest is the lender’s charge for that balance. Property tax, homeowners insurance, homeowners association dues, and mortgage insurance can add to your housing budget without reducing the loan.

This calculator separates principal and interest from those other costs so you can see which expenses actually build equity. The mortgage insurance input is a fixed monthly estimate; actual premiums and cancellation rules can vary.

How mortgage payments are calculated

For a fixed-rate loan, the scheduled principal-and-interest payment is P × r ÷ [1 − (1 + r)⁻ⁿ], where P is the initial loan balance, r is the monthly interest rate (annual percentage rate divided by 1,200 when entered as a percent), and n is the number of monthly payments. At zero interest, the payment is P ÷ n.

Each month, interest is calculated on the remaining balance. The rest of the principal-and-interest payment reduces what you owe. That is why more of an early payment goes toward interest and more of a later payment goes toward principal.

Worked example: a $400,000 home

With a $400,000 purchase price, $80,000 down, 6% annual fixed interest, and a 30-year term, the initial loan is $320,000. The scheduled principal-and-interest payment is approximately $1,918.56 per month, before property taxes, insurance, association fees, or mortgage insurance.

Try adding $200 per month toward principal. The results panel calculates the revised payoff schedule and interest difference rather than assuming every extra payment has the same effect.

What the estimate cannot tell you

This is a planning model for a fixed-rate loan with monthly payments. It does not calculate closing costs, lender fees, escrow changes, changing insurance premiums, prepayment penalties, variable interest rates, taxes on property transfers, or country-specific compounding conventions. The scheduled payment uses the entered rate as the loan’s nominal annual interest rate, not a lender’s APR including fees.

Confirm loan terms with your lender. For Canadian mortgages, the interest conversion and payment conventions can differ, so this US-style monthly-compounding model should not be used as a Canadian lender quote.

How to compare two mortgages fairly

Start with the same home price, down payment and estimated ownership costs. Change one loan assumption at a time so the comparison answers a specific question instead of mixing several effects together.

Compare the payment you must make

A shorter term typically raises the required principal-and-interest payment. Compare that amount against a realistic monthly budget including taxes, insurance, maintenance and an emergency cushion. A payment that looks affordable on paper may leave too little flexibility.

Compare lifetime interest and payoff date

A lower required monthly payment can cost more over the full loan. Examine total interest, the time until payoff and the amount of additional principal required to reach your preferred date. The savings shown by this tool assume the selected extra payments are credited toward principal on schedule.

Compare the risks, not just the headline

Ask whether each loan uses the same fixed rate, what closing costs and lender fees apply, whether extra payments are restricted, and how much cash you would keep available. If rates or fees differ, use each lender's actual quote rather than assuming identical terms.

Try this: Enter a 30-year term and note the payment and total interest. Change only the term to 15 years and compare again. Then return to 30 years and use the target-payoff feature to see what extra monthly principal might achieve a similar timeline. Read our 15-year versus 30-year comparison for the trade-offs.

Frequently asked mortgage questions

Does paying extra principal lower my required monthly mortgage payment?

Usually not on a standard fixed-rate mortgage. Extra principal payments reduce the remaining balance and can shorten the payoff timeline and total interest, but do not automatically change the lender’s required scheduled payment. Check your loan agreement for restrictions and prepayment penalties.

Does the monthly payment include property taxes and insurance?

The housing-cost estimate includes the yearly taxes and insurance that you enter, divided by twelve, as well as any monthly association dues and mortgage insurance you enter. These expenses do not reduce the principal balance and may change over time.

How is the extra-payment interest savings calculated?

The calculator models each monthly payment using the outstanding balance and fixed monthly interest rate. It then compares the normal repayment schedule with the schedule that adds your chosen amount toward principal each month.

Can I download the mortgage amortization schedule?

Yes. Use the Download CSV button next to the amortization table to save every month of principal, interest, payment and remaining loan balance for your current inputs. The exported table is an estimate, not a lender statement.