How to Use the Mortgage Calculator UK
Buying a home is one of the biggest financial decisions you'll ever make, and understanding your true costs — from monthly repayments to stamp duty — is essential. This calculator is designed to give you an instant, accurate picture of your mortgage affordability for the 2025–26 UK property market.
Start by entering the property price and your deposit amount. Next, enter the interest rate you've been quoted (or use the current average rate of around 4.5% for a benchmark). Choose your mortgage term— longer terms mean lower monthly payments but more total interest. If you're a first-time buyer, tick the box to see your stamp duty relief. The results show your monthly repayment, total repayment over the full term, total interest paid, stamp duty, and loan-to-value ratio.
Detailed Mortgage Formula Breakdown
Monthly Repayment Formula
Monthly payments are calculated using the standard amortisation formula: M = P × [r(1+r)ⁿ] ÷ [(1+r)ⁿ − 1] where M is the monthly payment, P is the loan amount, r is the monthly interest rate (annual rate ÷ 12), and n is the number of monthly payments (term × 12). For example, a £240,000 loan at 4.5% over 25 years: r = 0.00375, n = 300, M = £1,334 per month.
Stamp Duty (SDLT)
Stamp Duty Land Tax in England and Northern Ireland is a progressive tax: 0% on the first £250,000, 5% on £250,001–£925,000, 10% on £925,001–£1.5M, and 12% above £1.5M. First-time buyers get relief: 0% on the first £425,000 (up to £625,000 property price). For a £400,000 property, the SDLT is £7,500 for a non-first-time buyer (0% on £250k = £0, 5% on £150k = £7,500).
Loan-to-Value (LTV) Ratio
LTV = Loan Amount ÷ Property Price × 100. A lower LTV (higher deposit) typically qualifies you for better interest rates. At 60% LTV (40% deposit), you'll get the best rates. At 90% LTV (10% deposit), rates are higher and you may need to pay Mortgage Indemnity Guarantee (MIG) fees.
Real-Life Examples
Example 1 — £300,000 Property, 20% Deposit, 4.5% Rate, 25-Year Term
Property: £300,000. Deposit: £60,000 (20%). Loan: £240,000. At 4.5% over 25 years, your monthly payment is £1,334. Total repayment over the term: £400,267. Total interest: £160,267. Stamp duty: £2,500 (0% on first £250k, 5% on £50k). LTV: 80%. A solid standard scenario for first-time buyers in much of England.
Example 2 — £500,000 Property, 10% Deposit, 5% Rate, 30-Year Term
Property: £500,000. Deposit: £50,000 (10%). Loan: £450,000. At 5% over 30 years, your monthly payment is £2,416. Total repayment: £869,807. Total interest: £419,807. Stamp duty: £12,500 (0% on £250k, 5% on £250k). LTV: 90%. You may also need MIG insurance at this LTV, adding roughly £50–100 to your monthly costs.
Key Things to Know About UK Mortgages in 2025–26
- Interest rates: The Bank of England base rate influences mortgage rates. In 2025–26, average 2-year fixed rates are around 4.5%, with 5-year fixed rates slightly lower at 4.2%.
- Stamp Duty thresholds: The £250,000 0% band was made permanent in 2022. First-time buyer relief up to £425,000 is also now permanent.
- Affordability checks: Most lenders cap borrowing at 4.5× your annual income. Some go up to 5.5× for high earners or professionals.
- Mortgage term: 25 years is standard, but 30–40 year terms are increasingly common to keep monthly payments affordable — at the cost of more total interest.
Frequently Asked Questions
Q: How much deposit do I need for a mortgage in the UK?
A: Most lenders require at least 5% deposit (95% LTV), but 10% gives you access to much better rates. For the best rates, aim for 20-25% deposit (75-80% LTV). First-time buyers can take advantage of 95% mortgage schemes backed by the government.
Q: What is stamp duty and how much will I pay?
A: Stamp Duty Land Tax (SDLT) is a tax on property purchases in England and Northern Ireland. You pay 0% on the first £250,000, 5% on £250,001–£925,000, 10% on £925,001–£1.5M, and 12% above £1.5M. First-time buyers get relief up to £425,000. Use TheMetricApp.com for an instant, accurate result.
Q: How much can I borrow for a mortgage?
A: Most lenders offer 4–4.5× your annual income. For a joint application, it's typically 4× the higher income plus 1× the lower income, or 4.5× combined. Some lenders use more flexible affordability assessments. Use a mortgage affordability calculator to estimate your maximum borrowing.
Q: Should I choose a 2-year or 5-year fixed rate?
A: A 2-year fix offers lower initial rates and flexibility to remortgage sooner. A 5-year fix provides payment stability but typically has slightly higher rates and early repayment charges if you want to switch. If you expect rates to fall, a 2-year fix is better. If you want certainty, choose 5 years.
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