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🏠 Mortgage Calculator

Calculate your monthly repayment, total interest, and full amortisation schedule for any home loan.

UK reader? Use the UK mortgage repayment calculator for monthly-in-arrears UK conventions, or the overpayment calculator for the 10% ERC-free rule.

Home › Mortgage Calculator

Calculate your monthly repayment, total interest, and full amortisation schedule for any home loan.

How is a mortgage payment calculated?

A standard fixed-rate mortgage uses the amortising annuity formula: M = P × r(1+r)n / ((1+r)n−1), where P is the loan amount, r is the monthly interest rate (annual ÷ 12), and n is the total number of monthly payments. Most of each early payment goes to interest; the principal share grows over time.

Your Mortgage Details
Your Mortgage Summary
$0
Monthly P&I Payment
$0
Total Monthly (incl. tax & ins.)
$0
Total Interest Paid
$0
Total Cost of Loan
Mortgage Summary
ItemValue
Amortisation Schedule (first 24 months)
MonthPaymentPrincipalInterestBalance

How to use this calculator

Takes about 3 minutes.

  1. Enter the home price and your down payment
  2. Set the annual interest rate and the loan term in years
  3. Optionally add monthly property tax and home insurance to get a full PITI figure
  4. Click Calculate to see your monthly payment, total interest, and full amortisation schedule
  5. Adjust the down payment or term and recalculate to compare scenarios

Try these scenarios

Tap a scenario to load it into the calculator above.

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Methodology & Sources

This calculator implements the standard mortgage amortisation formula: M = P × [r(1+r)^n] / [(1+r)^n − 1]. Region-specific tax and rate defaults are sourced directly from each country's primary government source and reviewed against the publication date below.

  • USA: IRS — federal income tax brackets and contribution limits.
  • UK: GOV.UK — HMRC personal allowance, National Insurance, and dividend rates.
  • SA: SARS — personal income tax brackets and tax rebates.

Last verified: May 2026.

Key concepts

Principal vs. interest. Every mortgage payment is split between principal (reducing what you owe) and interest (the lender's fee). Early in a 30-year loan, most of each payment is interest; only after 15+ years does principal start dominating — this is the amortisation curve.

LTV (loan-to-value). Your loan divided by the home's price. A 20% deposit gives an 80% LTV. In the US, an LTV above 80% triggers Private Mortgage Insurance (PMI); in the UK, lower LTV typically unlocks better rates (FCA rules).

Fixed vs. variable rate. A fixed rate locks your payment for the fix period (typically 2, 5, or 10 years in the UK; whole-term in the US). A variable rate moves with central-bank policy — cheaper when rates fall, painful when they rise.

PITI and escrow. In the US, lenders often bundle property tax and homeowner's insurance into your monthly payment via an escrow account — Principal, Interest, Taxes, Insurance. The calculator's optional fields add these for a true monthly housing cost.

Total interest paid. Over a 30-year, $400k loan at 7%, you may pay more in interest than the home cost. Shortening to 15 years roughly halves total interest at the cost of a higher monthly payment.

Frequently Asked Questions

How is a mortgage payment calculated?
Your principal and interest payment uses the formula M = P × r(1+r)⊃n / ((1+r)⊃n − 1), where P is the loan amount, r is the monthly interest rate (annual rate ÷ 12), and n is the total number of payments (years × 12). This gives a fixed payment that fully repays the loan over the term.
How much deposit do I need?
In the USA, a 20% down payment avoids Private Mortgage Insurance (PMI). In the UK, most lenders require 5–10% with better rates at 25%+. In South Africa, banks typically require 10% though 100% bonds are sometimes available to qualifying first-time buyers. A larger deposit always reduces your monthly payment and total interest.
Should I choose a 15 or 30 year mortgage?
A 15-year mortgage has higher monthly payments but you pay significantly less interest overall — often less than half. A 30-year mortgage offers lower monthly payments and cash flow flexibility. If you can comfortably afford the 15-year payment, you will build equity much faster and save substantially on interest.
South Africa: What is transfer duty?
Transfer duty is a government tax on property transfers. Properties up to R1,100,000 are exempt. Above that, rates range from 3% to 13% on a sliding scale. Transfer duty is a once-off cost paid by the buyer on registration and is separate from your monthly bond repayment.
UK: What is stamp duty?
Stamp Duty Land Tax (SDLT) is paid on property purchases in England and Northern Ireland. From April 2025, the nil-rate threshold returns to £125,000 (2% on £125k–£250k, 5% on £250k–£925k). First-time buyers get relief up to £425,000 until March 2025, then £300,000. Scotland and Wales have their own equivalent taxes.
USA vs UK vs South Africa: how do mortgage interest rates differ?
USA: 30-year fixed dominates (~6–7% in 2026), backed by Fannie Mae/Freddie Mac standardised products. UK: 2-, 5-, and 10-year fixes are the norm (~4–5%), then borrowers must remortgage or revert to a variable Standard Variable Rate. South Africa: most bonds are linked to prime (currently ~11%) with limited fixed-rate options. The same loan size carries very different lifetime interest in each market.
What's the most common mortgage mistake first-time buyers make?
Maxing out 'how much can I borrow?' instead of 'how much should I borrow?' Lenders often approve at 4–4.5× income but spending the full amount leaves no margin for rate rises, repairs, or income shocks. A safer rule: keep total housing costs (PITI + maintenance) under 28% of gross income, and don't exhaust your savings on the deposit — keep 3–6 months of expenses in cash.
What happens if my mortgage rate rises during a fixed term ending?
At the end of a UK fix, your rate rolls to the lender's Standard Variable Rate (often 2–4% above your fixed rate) unless you remortgage. In the USA, the 30-year fixed never resets. ARM borrowers face the same risk at each reset point. Use the calculator with the new rate to see your new monthly payment — for many UK borrowers a fix-to-fix increase of 2 points raises monthly cost by £200–£400 on a typical £200,000 loan.
I have my monthly payment — now what?
Compare it against your gross monthly income: housing costs above ~28% will squeeze other goals. Then stress-test: rerun the calculator with the rate 2 points higher to confirm you can still afford the loan if you remortgage at a worse rate. Finally, decide whether to overpay — even £100 a month extra on a 25-year £200k mortgage at 5% shaves about 3 years and £15,000 of interest.
Mortgage vs renting — which builds wealth faster?
Depends on rate, term, deposit, and house-price growth. Renting + investing the deposit difference can beat buying if rents stay low and equity returns exceed both house-price growth and your mortgage rate. Buying tends to win when (a) you stay 7+ years, (b) house prices keep pace with inflation, and (c) the mortgage rate is below long-run equity returns. Use this calculator alongside an investment-growth calculator to compare scenarios on your numbers.

Written and maintained by , Founder & Editor, FinCalcHub.

Last reviewed: · See editorial policy

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