Mortgage Calculator — Work Out Your Monthly Payment & Total Interest (Free Tool)

Adrian Cole October 29, 2026

Mortgage Calculator

Short answer: Your monthly mortgage payment (principal and interest) depends on four numbers: the home price, your down payment, the annual interest rate, and the loan term. A $300,000 home with a $60,000 down payment, borrowed at 6.5% over 30 years, costs $1,516.96 a month in principal and interest — $546,105.60 in total, of which $306,105.60 is interest. Enter your numbers below and this free calculator shows your monthly payment, total paid and total interest before you make an offer.

Last updated: 29 October 2026 · Estimate only — not financial advice. This calculator shows principal and interest only; property tax, homeowner's insurance, PMI and HOA dues are not included (see below).

The amount you pay up front. Your loan amount is the home price minus this figure. A 20% down payment on a $300,000 home is $60,000.

The fixed interest rate on the mortgage — not the APR. If you only have the APR, see the FAQ below.

How the math works

  • Loan amount = home price − down payment. A $300,000 home with $60,000 down means a $240,000 mortgage.
  • Monthly interest rate = annual rate ÷ 12. A 6.5% annual rate means about 0.5417% a month.
  • Number of payments = years × 12. A 30-year mortgage has 360 monthly payments.
  • Monthly payment (principal and interest) = loan amount × monthly rate × (1 + monthly rate)payments ÷ ((1 + monthly rate)payments − 1). This is the standard amortizing-loan formula: every payment covers that month's interest first, and the rest pays down the balance, so the interest part shrinks and the principal part grows over time.
  • Zero-interest edge case: if the rate is 0%, the payment is simply loan amount ÷ number of payments, and the total equals the amount borrowed.
  • Total paid = monthly payment (rounded to cents) × number of payments, so the figures in the result add up exactly. Total interest = total paid − loan amount.

Worked example (illustrative — not a real person's mortgage, not advice)

You buy a $300,000 home with a $60,000 (20%) down payment, borrowing $240,000 at 6.5% annual interest over 30 years (360 payments):

  • Loan amount: $300,000 − $60,000 = $240,000
  • Monthly rate: 6.5% ÷ 12 = 0.5417% (0.0054167)
  • Monthly payment (principal and interest): $1,516.96
  • Total paid: $1,516.96 × 360 = $546,105.60
  • Total interest: $546,105.60 − $240,000 = $306,105.60

Notice something sobering: over 30 years you pay more in interest ($306,105.60) than you borrowed ($240,000). Now take the same $240,000 loan over 15 years instead: the monthly payment rises to $2,090.66, but the total paid falls to $376,318.80 and the interest to $136,318.80 — a saving of $169,786.80 in interest. That is the 15-year trade-off in one line: a heavier monthly payment, a much cheaper loan overall.

What this calculator does NOT include

Most real mortgage bills are higher than the principal-and-interest figure above, because lenders usually collect four extra items with the payment (often called PITI plus PMI and dues): property tax, homeowner's insurance, private mortgage insurance (PMI) if your down payment is under 20%, and HOA dues where they apply. Those vary by location, home and lender, so no single calculator can include them honestly without your local figures. Treat the result here as the loan's core cost, then add your local tax, insurance and PMI estimates for the full monthly picture.

FAQ

15 years or 30 years — which term should I pick?
A 30-year term gives the lower monthly payment and more breathing room, but far more total interest (see the worked example: $306,105.60 vs $136,318.80 on the same $240,000 loan). A 15-year term costs more each month but builds equity much faster and ends the debt 15 years sooner. Run both terms in the calculator with your own numbers, and only pick the 15-year payment if you can still cover taxes, insurance and an emergency fund comfortably.

Interest rate vs APR — which number do I enter?
Enter the interest rate, not the APR. The APR is a broader cost measure that folds in fees (origination fees, points, some closing costs) and is usually slightly higher than the interest rate. This calculator does not model fees, so entering the APR would overstate the payment. Compare APRs across lenders to judge total cost, but run the payment math on the interest rate.

What happens if my down payment is under 20%?
You can usually still buy — many loans allow far less than 20% down — but the lender will normally add private mortgage insurance (PMI) to your monthly bill until you build enough equity (often 20%), and you borrow more, so the payment and total interest both rise. Try it in the calculator: a $0 down payment on the same $300,000 home at 6.5% over 30 years gives $1,896.20 a month and $382,632.00 of interest, before PMI.

Would paying extra each month actually help?
Yes — any extra payment goes straight to principal (tell your lender to apply it that way), which cuts the balance, cuts future interest, and shortens the loan. Even $100 extra a month on the worked example above saves tens of thousands in interest over 30 years. This calculator shows the scheduled payment only; it does not model extra payments.

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Disclaimer: This tool gives a simplified mortgage estimate for education only. It is not financial advice, and it does not include property tax, homeowner's insurance, PMI, HOA dues, fees or variable-rate changes. Your lender's actual payment may differ — always check the loan agreement.

— Adrian Cole, Bia Crypto

 

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