Starlight Tools

Mortgage Repayment Calculator: Monthly Payments, Interest, and Amortization

Calculate your monthly mortgage repayment, total interest, payoff date, deposit and loan amount, and amortization schedule. Add taxes, insurance, service charges, overpayments, and affordability context for a fuller housing-cost estimate.

Mortgage details

Calculation mode
Property price and deposit
Calculated mortgage amount £297,500.00 Loan-to-value: 85.0%. Deposit is at least 10%, but below 20%.
Use this directly for remortgage/refinance or if you already know the amount.
Enter a positive number of years or months.
Optional monthly housing costs

These are estimates and are kept separate from principal and interest.

Overpayments

Estimate voluntary overpayments. Check your lender for annual limits, fees, or early repayment charges.

Affordability context

Educational estimate only. Actual approval depends on lender criteria, credit profile, property, fees, and local rules.

Results

Use the example mortgage details or enter your own figures, then click Calculate. Results will appear here.

How to use this mortgage repayment calculator

  1. Choose purchase, remortgage, or known mortgage amount mode.
  2. Enter the property price and deposit, or enter the mortgage amount directly.
  3. Enter the annual interest rate, term, currency, and start month.
  4. Optionally add ownership costs, overpayments, and affordability details.
  5. Calculate to see monthly repayment, total interest, payoff date, housing cost, and amortization.

Mortgage repayment guidance

How interest affects your repayment

A repayment mortgage splits each payment between interest and principal. Early payments usually contain more interest because the outstanding balance is higher. As the balance falls, more of each payment reduces principal.

How overpayments reduce total interest

Extra payments reduce the balance sooner, which means less interest accrues in later months. The calculator estimates the new payoff date and interest saved, but lender overpayment limits and fees can change the real result.

Repayment vs interest-only mortgages

This tool models a repayment mortgage. Interest-only mortgages work differently: payments cover interest during the term and the borrowed principal must be repaid separately.

What this calculator includes and excludes

It includes principal and interest, and any optional monthly costs or overpayments you enter. It does not include lender fees, taxes that vary by location unless entered, rate changes, escrow rules, or lender-specific underwriting.

Assumptions and accuracy

  • Assumes a fixed-rate repayment mortgage with monthly payments and monthly interest calculation.
  • Taxes, council tax, insurance, PMI, HOA, service charge, and other costs are estimates only if you enter them.
  • Fees, offset accounts, daily interest, payment holidays, rate changes, and lender-specific rules may produce different figures.
  • Your inputs stay in your browser. No mortgage data is sent to a server by this calculator.
  • Results are informational and educational, not financial, tax, legal, or lending advice.

Formula/content last reviewed: July 5, 2026.

Mortgage repayment calculator FAQ

How are mortgage repayments calculated?

For a fixed-rate repayment mortgage, the calculator uses the standard amortization formula based on loan amount, monthly interest rate, and number of monthly payments.

What do principal and interest mean?

Principal is the amount borrowed and repaid over time. Interest is the borrowing cost charged on the outstanding balance.

Are taxes and insurance included?

Principal and interest are calculated automatically. Taxes, insurance, mortgage insurance, HOA or service charge, and other ownership costs are included only if you enter them.

What does APR mean?

APR means annual percentage rate. This calculator treats the rate as a fixed annual interest rate for repayment estimates and does not add lender fees unless you include them separately.

How does my deposit affect repayment?

A larger deposit reduces the mortgage amount and loan-to-value ratio, which usually lowers the monthly repayment and total interest.

What happens if I make overpayments?

Overpayments reduce the balance faster, which can cut the payoff date and reduce total interest. Check lender rules for limits or early repayment charges.

What is the difference between repayment and interest-only mortgages?

A repayment mortgage pays interest and gradually reduces principal. An interest-only mortgage pays interest during the term and leaves the principal to be repaid separately.

Why might a lender quote differ?

Lender quotes may include fees, daily interest rules, insurance, taxes, rate changes, rounding, eligibility criteria, or payment timing that this estimate does not model.

Can this calculator work for refinancing or remortgaging?

Yes. Choose the known mortgage amount option or remortgage mode and enter the current balance, rate, term, and start month for an estimate.

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