Mortgage Calculator

1. Enter the home price, down payment, annual interest rate, and loan term.
2. Optionally enter property tax, home insurance, HOA, and mortgage insurance. Blank optional fields are treated as zero.
3. Choose Amortization schedule for the standard schedule, or Extra-payment payoff to model additional principal.
4. In payoff mode, enter a recurring extra amount, a one-time amount, or both. For a one-time payment, enter the month number; month 1 is the first payment.
5. Click Calculate to create the payment, assumptions, comparison, and schedule. The loan amount is calculated when you activate this control, not as fields change.
6. Use Copy result or Download result (.txt) after calculation. If copying is unavailable, select and copy the displayed text manually.
7. Click Reset to clear the fields, return to Amortization schedule mode, hide errors, and hide the result.

What the Results Show

The displayed total monthly payment is the initial total: principal and interest plus the optional tax, insurance, HOA, and mortgage insurance amounts included for the starting balance. The assumptions table lists the values used, and the result also includes the formula, payoff comparison when applicable, full amortization schedule, and plain-text output.

In the schedule, the Principal & interest column is the loan payment. Schedule rows do not show a total housing payment that includes taxes, insurance, or HOA. In payoff mode, the comparison reports payoff time in months or years and how many months earlier the loan ends; it does not calculate a calendar date.

The Mortgage Payment Formula

The loan amount is the home price minus the down payment:

Loan amount = Home price - Down payment

The annual rate is converted into a monthly rate:

r = Annual rate / 100 / 12

The fixed monthly principal and interest payment fully amortizes the loan amount over n monthly payments. The calculator sets n to the entered term in years multiplied by 12, rounded to the nearest whole payment:

Payment = Loan amount x r / (1 - (1 + r)^-n)

At a 0% annual rate, it uses Payment = Loan amount / n.

For each month, interest and principal are split, and the balance is updated:

Interest = Remaining balance x r
Principal = Payment - Interest
Remaining balance = Remaining balance - Principal - Extra payment

For example, a $350,000 home with a $70,000 down payment gives a $280,000 loan. At 6.5% annual interest over 30 years, r = 0.065 / 12 = 0.005417 and n = 360, producing a fixed monthly principal and interest payment of about $1,769.

Taxes, Insurance, HOA, and Mortgage Insurance

Property tax and home insurance are entered as annual amounts and divided by 12 to get a constant monthly add-on. HOA fees are entered directly as a monthly amount. None of these amortize - they are added on top of the principal and interest payment every month at the same rate you entered, since they are not part of the loan balance.

Monthly mortgage insurance (PMI) is entered as a flat monthly amount. In this calculator, PMI remains active while the starting balance is greater than 80% of the entered home price. It is dropped once the balance reaches 80% or less, and it is not added again later in the schedule.

Extra-Payment Payoff Mode

In this mode, any recurring monthly extra amount is added to principal every month, and any one-time extra amount is added to principal in the specific month number you choose. The calculator builds this "extra payments" schedule alongside the standard schedule and reports payoff time, months earlier, years or months of payoff time, and total interest saved.

The one-time-payment month must be at least 1, but it is not checked against the loan term. A month beyond the generated schedule is accepted and has no effect.

Assumptions and Unit Conventions

• Fixed rate, fixed schedule: the rate and the principal and interest payment stay constant for the life of the loan - this tool does not model adjustable rates, rate resets, or promotional periods.
• Monthly payments only: all calculations use 12 payments per year, matching standard mortgage billing.
• Constant escrow items: property tax, home insurance, and HOA fees are held constant for the full schedule - no reassessments, premium changes, or fee increases are modeled.
• PMI removed at 80% of entered home price: the calculator drops mortgage insurance once the balance reaches 80% or less of the entered home price, and does not re-add it afterward.
• Extra payments applied entirely to principal: recurring and one-time extra amounts reduce the balance directly and are never diverted to interest or escrow.

Input Validation

The calculator checks that: the home price is greater than 0; the down payment is 0 or greater and less than the home price; the annual interest rate is between 0 and 100; the loan term is greater than 0 and produces no more than 720 monthly payments; and any optional tax, insurance, HOA, or extra-payment figures entered are 0 or greater. Blank optional fields are treated as zero. If any check fails, calculation stops and a specific error message is shown instead of a result.

Reading the Result

The result section shows the principal and interest payment, the initial total monthly payment including optional costs used for the starting balance, total interest over the life of the loan, and payoff time. A table below lists the assumptions used in the formula. In payoff mode, a comparison table shows the standard and extra-payment scenarios, including months earlier and interest saved. A full schedule table shows every month's principal and interest payment, principal portion, interest portion, any extra principal applied, the remaining balance, and whether PMI is still active that month.

Copy or Download the Result

Use Copy result to copy a plain-text summary and the full schedule to your clipboard, or Download result (.txt) to save the same summary and schedule as a .txt file for your records.

What This Tool Does Not Do

This calculator does not fetch live interest rates, lender records, credit data, or any personalized account information, and it is not financial, tax, or lending advice. It does not determine affordability, estimate loan approval odds, compare refinance offers, or model adjustable rates, closing costs, rate locks, or missed payments - it performs a single, transparent fixed-rate mortgage calculation on the numbers you provide. Use the dedicated affordability, refinance, or rent-vs-buy tools for those separate questions, and confirm exact figures with your actual lender or loan documents.

Privacy & Security

The mortgage calculation runs in your browser. The local calculation script contains no submission of the mortgage values you enter. The inspected page does not establish a broader site-wide claim about whether other shared page services receive information.

Frequently Asked Questions