UK Mortgage Calculator 2024-25
Calculate UK mortgage monthly payments, total interest, LTV, and affordability. Covers repayment and interest-only mortgages with the 4.5x income affordability rule.
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How to use this calculator
- 1
Enter the property price and your deposit. The loan is the price minus the deposit, and it is never negative.
- 2
Enter the term in years and the annual interest rate as a single figure; the tool does not model a rate that changes after an initial period.
- 3
Choose repayment, where each payment covers interest and capital, or interest-only, where each payment covers interest alone and the full loan is shown as repaid at the end.
- 4
Read the monthly payment, total interest and the minimum income line, which divides the loan by the 4.5 multiple built into the tool.
Frequently asked questions
What formula does this mortgage calculator use?
For repayment mortgages it uses the standard annuity formula with a monthly rate equal to the annual rate divided by 12 and a number of payments equal to years × 12. Interest-only simply multiplies the loan by the monthly rate, and the full loan is added back as a single repayment at the end. Rates are assumed to stay fixed for the whole term.
What does the “minimum income needed” line mean?
It divides the loan amount by 4.5. The multiple is a figure built into this tool, labelled 2024-25, and it is not a statement of what any lender requires. Lenders set their own multiples, apply their own affordability tests and look at debts, outgoings and credit history, none of which this tool considers.
How is loan-to-value worked out?
It is the loan divided by the property price, shown as a percentage, with the deposit shown as a share of the price on a separate line. A £300,000 property with a £60,000 deposit gives a loan of £240,000 and an LTV of 80.0%. If the deposit is at least the price, the loan and LTV show as zero.
Are fees, insurance or taxes included?
No. Arrangement fees, valuation and legal costs, early repayment charges, buildings insurance, mortgage protection, ground rent, service charges and stamp duty or equivalent land taxes are all outside the calculation. Only the loan, rate and term feed the payment.
Why does the interest-only total look so large?
Because the capital is never reduced during the term. The tool charges interest on the full loan for every month, then adds the loan back at the end as “total amount repaid”. For a £405,000 loan at 4.5% over 30 years that gives £1,518.75 a month and £546,750 of interest. It does not model how the capital would actually be repaid.
What happens with a 0% rate or other unusual inputs?
A rate of 0% is honoured: a repayment mortgage then just divides the loan by the number of months and shows zero interest. The boxes start at 5% and 25 years, and clearing one counts as 0: a 0% rate is honoured as above, and a term of 0, like any term below one year, is treated as one year. A zero price gives zero for every line instead of an error.
Do the figures change with the market?
The tool never looks up market rates. The default of 5% is simply a starting value, and the 4.5 multiple is fixed in the code. Lending rules and rates change continuously, the tool’s tables are not updated automatically, and a lender or qualified adviser governs what applies to your application.
UK mortgage payments: the annuity formula, LTV and a 4.5 times income check
How the monthly payment is calculated
The loan is the property price minus the deposit. For a repayment mortgage the tool applies the annuity formula: payment = loan × r × (1 + r)^n ÷ ((1 + r)^n − 1), where r is the annual rate divided by 12 and n is the term in months. That produces a level payment that clears the loan exactly at the end of the term. For interest-only, the payment is loan × r and the whole loan is added back as a final lump. Loan-to-value is loan ÷ price, and the minimum income line divides the loan by the 4.5 multiple built into the tool, labelled 2024-25.
Worked examples: repayment and interest-only
The default inputs are a £300,000 property, a £60,000 deposit, 25 years and 5%. The loan is £240,000 at 80.0% LTV, the payment is £1,403.02 a month, total repaid is £420,905 and total interest is £180,905; the 4.5 multiple implies £53,333 of income. Switching to a £450,000 property with a £45,000 deposit, 30 years, 4.5% and interest-only gives a loan of £405,000 at 90.0% LTV, £1,518.75 a month, £546,750 of interest and £951,750 in total once the loan is added back, with an implied income line of £90,000.
How the rate moves the payment
The table holds the £240,000 loan and 25-year term constant and changes only the interest rate. Each extra percentage point adds between about £129 and £143 a month and tens of thousands in total interest, and the increase grows as the rate rises because interest compounds on the outstanding balance.
| Annual rate | Monthly payment | Total interest paid |
|---|---|---|
| 3% | £1,138.11 | £101,432 |
| 4% | £1,266.81 | £140,043 |
| 5% | £1,403.02 | £180,905 |
| 6% | £1,546.32 | £223,897 |
Limits of a single-rate model
Real mortgages often have an initial fixed or tracker period followed by a different rate, and the payment changes when it ends. This tool applies one rate across the whole term, so the figures are best read as a comparison of scenarios. Fees, insurance, early repayment charges and land taxes are excluded, and the minimum income line is a simple division, not a lender’s affordability assessment.
About the built-in multiple
The 4.5 income multiple and the default 5% rate are figures built into this tool, labelled 2024-25. Lending criteria and market rates change constantly and the tool’s tables are not updated automatically, so a lender, or a qualified adviser, governs what applies to any application.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →