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CalcStudioPro

Mortgage Calculator

Calculate monthly mortgage payments, total interest, and payoff time with optional extra payments.

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Dr. Lena Westbrook, CFA
Personal Finance Economist · Reviewed by Marcus Hale, Licensed Mortgage Advisor
Updated 2026-04-19

Inputs

Optional. Additional amount paid each month reduces total interest.

Results

Monthly payment
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Your scheduled principal + interest payment
Total amount paid
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Total interest paid
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Months to payoff
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Years saved with extra payments
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Formula
M = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1]

A mortgage is the single largest financial commitment most households ever make. The monthly payment depends on three variables: how much you borrow, the interest rate, and how long you take to repay. This calculator computes your exact monthly payment and total interest, then shows how additional monthly contributions compress your payoff timeline.

How it works

The mortgage payment formula distributes your loan amount plus compounded interest evenly across each month of the term. Early payments go mostly to interest; later payments go mostly to principal. This is why making extra payments early has an outsized impact — every extra dollar applied to principal avoids years of compound interest on that dollar.

Formula
M = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1]
Where M = monthly payment, P = principal (loan amount), r = monthly interest rate (annual rate ÷ 12), and n = total number of payments (years × 12).

Worked example

On a $300,000 loan at 6.5% for 30 years, your monthly payment is $1,896.20. Over 30 years you pay $682,633 total — $382,633 of that is interest, more than the loan itself. Adding just $200 extra per month shortens the loan by about 6 years and saves roughly $95,000 in interest.

What affects your mortgage payment

Four factors dominate: loan amount (principal), annual interest rate, loan term, and any extra payments. A 1% difference in rate on a $300,000 30-year mortgage changes your payment by roughly $180/month and your lifetime interest by over $70,000. Shorter terms (15 years instead of 30) raise the monthly payment but drastically reduce total interest — often by half.

How extra payments compound savings

Each extra dollar of principal removes not just itself from the loan, but also all future interest that would have accumulated on it. On a 30-year loan at 6.5%, an extra $100/month reduces the payoff time by about 4 years and saves roughly $55,000. Unlike refinancing, extra payments have no closing costs and can be stopped or adjusted any time.

Taxes, insurance, and PMI

This calculator shows principal and interest only. Real monthly housing costs also include property taxes (typically 0.5–2.5% of home value annually), homeowner's insurance, and private mortgage insurance (PMI) if your down payment was under 20%. Add these separately to plan your true monthly housing budget.

Fixed vs. adjustable rate

This calculator assumes a fixed-rate mortgage — the rate stays constant for the entire term. Adjustable-rate mortgages (ARMs) start lower but can reset higher after an initial period (commonly 5, 7, or 10 years). For ARMs, your real lifetime cost depends on rate movements that cannot be known in advance.

Frequently asked questions

Does this include property taxes and insurance?
No. This calculator shows principal and interest only. Your actual mortgage payment (PITI) will be higher because it includes property taxes, homeowner's insurance, and possibly PMI. Add those separately when budgeting.
How much home can I afford?
A common rule: your total monthly housing cost (including taxes and insurance) should not exceed 28% of your gross monthly income. A household earning $8,000/month should aim for total housing costs under $2,240.
Is it better to take a 15-year or 30-year mortgage?
A 15-year mortgage saves enormous interest but requires a higher monthly payment. If you can afford the higher payment without straining other financial goals (retirement, emergency fund), 15 years is mathematically superior. If not, a 30-year with extra payments gives flexibility.
What's a good interest rate?
Rates vary by economic conditions, your credit score, and loan type. As of 2026, rates between 6–7% are typical for qualified buyers in the US on a 30-year fixed. Shop at least three lenders — differences of 0.25% matter significantly over 30 years.
Should I refinance?
Generally worth considering when current rates are at least 0.75–1% below your existing rate, and you plan to stay in the home long enough to recover closing costs (typically 2–5% of the loan amount). Use our refinance calculator to see the specific numbers.

References