Mortgage Calculator
Estimate monthly payments, total interest and the effect of overpayments. Figures update as you type. This is not a quote from a lender.
Optional overpayments
Stamp duty estimate (England & NI)
Uses residential SDLT bands in force from April 2025. Not for Scotland or Wales.
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Interest-only: the monthly figure covers interest. The borrowed amount is still due at the end of the term unless you overpay.
With overpayments
If the rate moved
Rate 1 of 1
Year-by-year balance
| Year | Paid | Interest | Left |
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Estimate only. Lenders add fees, product rates and stress tests. Stamp duty here is England and Northern Ireland residential bands from April 2025. Confirm on GOV.UK before you exchange.
How to use the Mortgage Calculator
- Enter the Property price and Deposit. You can type the deposit in pounds or as a percentage.
- Set the Interest rate, Term and whether the loan is Repayment or Interest only.
- Optional: open Overpayments or Stamp duty estimate.
- Figures update as you type. Use the rate arrows to see a higher or lower rate, and open Year-by-year balance for the rundown.
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What it is for
A repayment mortgage pays interest and some of the capital each month so the balance should reach zero at the end of the term. Interest-only pays the interest and leaves the borrowed amount outstanding unless you overpay. This page runs that arithmetic and, if you add extra payments, estimates interest and time saved.
Loan to value is the mortgage divided by the price. Lenders price deals in LTV bands; the note under the summary is a rule of thumb, not an offer. Stamp duty uses England and Northern Ireland residential bands from April 2025. Scotland and Wales use different taxes. Confirm the bill on GOV.UK before you exchange.
Why it runs in your browser
The numbers stay in the tab. Catpool does not store the price, deposit or rate, and this is not an application to a lender.
A worked example
Take a £250,000 home with a £25,000 deposit. That is a 10% deposit, so the loan is £225,000 and the loan to value is 90%.
- On a repayment mortgage at 4.5% over 25 years, the monthly payment comes to about £1,251. Over the full term you would pay roughly £150,000 in interest on top of the £225,000.
- Overpaying £100 a month from the start would clear the loan in about 21 years and 10 months, saving around £21,500 in interest, if the lender allows it without charges.
- Interest-only at the same rate would be about £844 a month, but the full £225,000 would still be owed at the end.
- Stamp duty in England and Northern Ireland at standard rates would be £2,500. A first-time buyer would pay nothing at this price.
Try changing one thing at a time, such as a bigger deposit or a shorter term, and watch how the monthly figure and the total interest move. The rate arrows show how much a small change in rate matters.
Common questions
Is the monthly figure what my lender will charge?
No. It ignores product fees, valuation fees, account fees and any discount or tracker change after a fixed period. Treat it as a planning number.
What does interest-only actually repay?
The monthly amount is the interest on the balance. The original loan is still due at the end of the term unless overpayments have reduced it. The note under the type field repeats that.
Do overpayments always save that much interest?
Only if the lender accepts them without an early-repayment charge and applies them to the balance. Many deals cap how much you can overpay each year.
Why is first-time buyer stamp duty zero on a £250,000 home but not on a £600,000 one?
Relief applies up to £300,000, with 5% on the slice to £500,000. Above £500,000 the relief does not apply at all and standard bands are used on the whole price.
Can I use this in Scotland or Wales?
The mortgage maths still works. The stamp duty box does not. Use Revenue Scotland or the Welsh LTT calculator for that tax.
Related: Calculators, Percentage Calculator, About.
