UK Mortgage Calculator – Estimate Repayments & Stamp Duty

Buying a property in the UK involves two separate costs to plan for: your monthly mortgage repayment and the one-off Stamp Duty Land Tax (SDLT) due on completion. This calculator estimates both, using your property price, deposit, interest rate and mortgage term, alongside your buyer type to apply the correct SDLT bands.

Choose between a repayment mortgage, where each instalment reduces both capital and interest, or an interest-only mortgage, where you repay only the interest each month and clear the capital separately at the end of the term. The results also show your Loan-to-Value (LTV) ratio and a year-by-year amortisation schedule.

02How Stamp Duty Land Tax (SDLT) is calculated

SDLT is charged in bands on the portion of the price that falls within each threshold, similar to income tax. The rate you pay also depends on whether you're a first-time buyer, moving home, or purchasing an additional property such as a buy-to-let or second home.

• First-time buyers get relief on properties up to a set price threshold, reducing or removing SDLT entirely below that band
• Home movers pay standard residential SDLT rates on the full purchase price
• Additional properties (buy-to-let or second homes) attract a surcharge on top of the standard rates
• This calculator estimates SDLT for England and Northern Ireland — Scotland uses Land and Buildings Transaction Tax (LBTT) and Wales uses Land Transaction Tax (LTT), both with different bands

03Loan-to-Value (LTV) and why it matters

LTV is your mortgage amount as a percentage of the property price. A bigger deposit means a lower LTV, which typically unlocks better interest rates — lenders reserve their cheapest fixed and tracker rates for borrowers below 60–75% LTV, with rates stepping up as LTV rises towards 90–95%.

04Example

On a £300,000 property with a 10% deposit (£30,000) and a 5% rate over 25 years, the repayment mortgage works out at roughly £1,570 a month. As a home mover, SDLT on that purchase would be around £5,000, due separately at completion — a cost worth budgeting for alongside your deposit and moving costs.