Plot No. 2 · Money & Finance
Mortgage Repayment Calculator
Estimate your monthly mortgage payment, the total you'll repay over the term and how much of that is interest. Enter your loan amount, interest rate and term in years.
Assumes a fixed annual interest rate compounded monthly. Real mortgages may include fees, variable rates and overpayments that change the outcome.
The link saves your inputs so you can bookmark or share this exact result.
How the mortgage repayment calculation works
A repayment mortgage is paid off with a fixed monthly amount that covers both the interest charged that month and a slice of the capital you borrowed. This calculator uses the standard annuity formula to find that level payment from your loan amount, annual interest rate and term in years, then multiplies it out to show the total you will repay and how much of that is pure interest.
The key insight the totals reveal is how much interest stretches across a long term. Because interest is charged on the outstanding balance, a higher rate or a longer term both push the total interest up sharply, often by far more than the change to the monthly payment suggests at first glance.
How to use the mortgage calculator
- Enter the loan amount you plan to borrow, which is the property price minus your deposit.
- Set the annual interest rate offered by the lender.
- Choose the term in years, then read the monthly payment, total repaid and total interest.
Worked examples
A 250,000 loan at 4.5 percent over 25 years
Inputs: Loan amount 250,000, rate 4.5 percent, term 25 years.
Result: A monthly payment of about 1,390, a total repaid of roughly 416,874 and total interest of about 166,874 over the full term.
The same loan at 5 percent
Inputs: Loan amount 250,000, rate 5 percent, term 25 years.
Result: The monthly payment rises to about 1,461, only 71 more a month, yet total interest jumps to roughly 188,443. Half a percentage point adds over 21,000 across the term.
Limitations and common mistakes
Edge cases and limitations
- This models a fixed rate compounded monthly. Real mortgages often start on a fixed deal then revert to a variable rate, which this does not project.
- Arrangement fees, valuation fees, insurance and any early repayment charges are not included in the totals.
- Overpayments, payment holidays and offset accounts all change the outcome and are not modelled here.
Common mistakes
- Entering the property price instead of the loan amount. Subtract your deposit first.
- Comparing only monthly payments between two deals. A longer term lowers the monthly figure but can quietly add tens of thousands in interest.
Frequently asked questions
Is this for repayment or interest-only mortgages?
This calculator assumes a standard repayment mortgage where each monthly payment covers both interest and capital. Interest-only mortgages have a different structure where you only pay interest each month and repay the principal at the end.
How does the interest rate affect the total cost?
Even a small change in rate makes a big difference over 25 years. For example on a £250,000 loan, going from 4.5% to 5% adds roughly £75 to the monthly payment and about £22,000 to total interest.
Should I take a longer term to lower monthly payments?
Longer terms reduce the monthly payment but increase total interest paid. A 30-year term instead of 25 typically costs tens of thousands more over the full life of the loan.
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