Mortgage Repayment Calculator

Understanding UK Mortgage Repayments Before You Calculate

A mortgage is likely the single largest financial commitment you will make. In the UK, residential mortgages typically run for 25 to 35 years, and the total amount you repay depends on three key variables: the amount you borrow, the interest rate, and the term length. Even a small change in any of these figures can shift your total cost by tens of thousands of pounds.

Most UK homebuyers opt for a repayment mortgage, where each monthly payment covers both interest accrued that month and a portion of the outstanding capital. Over time, the capital balance falls to zero and the property is yours outright. The alternative is an interest-only mortgage, where monthly payments cover only the interest — the capital must be repaid separately at the end of the term, usually through selling the property, maturing investments, or other savings.

Interest rates in the UK are heavily influenced by the Bank of England base rate and the swap rates that lenders use to price fixed-rate deals. Since 2022, rates have risen significantly from historic lows, making it more important than ever to understand exactly what your monthly outgoings will be before committing. Lenders also tier their rates by loan-to-value (LTV) — the proportion of the property value you are borrowing. A larger deposit means a lower LTV, which typically unlocks better rates.

This calculator lets you enter your property price, deposit, interest rate, and term to see your exact monthly payment, the total interest paid over the life of the mortgage, and a year-by-year amortisation chart showing how each payment splits between capital and interest. You can toggle between repayment and interest-only to compare the two side by side. All figures are calculated in GBP and based on standard UK mortgage conventions — monthly compounding with no payment holidays.

How UK Mortgage Repayments Are Calculated

Every repayment mortgage monthly payment is calculated using the standard annuity formula. Given a loan amount P, monthly interest rate r (annual rate ÷ 12), and total payments n (term in years × 12):

Monthly payment = P × r × (1+r)^n ÷ ((1+r)^n − 1)

This produces a constant monthly payment throughout the term. In the early years, most of each payment is interest — because the outstanding balance is large. As the balance falls, the interest component shrinks and the principal portion grows. This pattern is called amortisation, and the year-by-year breakdown is what the chart above shows.

For a £224,000 mortgage at 4.5% over 25 years, the monthly payment is £1,238. In year 1, around £840 of each payment goes to interest and only £398 to principal. By year 25, almost all of each payment clears the remaining balance.

Repayment vs Interest-Only Mortgages

A repayment mortgage guarantees your debt is cleared by the end of the term. Each month you pay both the interest accrued and a slice of the capital. This is the most common type in the UK for residential buyers.

An interest-only mortgage requires only the interest each month, making payments lower. However, the capital balance does not reduce — you owe the same amount at the end as you did at the start. You are required to have a credible repayment vehicle (such as an ISA, investment portfolio, pension, or sale of the property) to clear the debt.

Interest-only is more common for buy-to-let landlords and some high-net-worth borrowers. Regulators have tightened rules considerably since the 2008 financial crisis, when many homeowners faced a repayment shortfall.

How Interest Rates Affect Monthly Payments

Even a 0.5% rate change has a significant effect over a 25-year term. The table below shows monthly payments on a £200,000 mortgage across common rate levels:

The difference between 3% and 6% on a £200,000 mortgage over 25 years is over £102,000 in total interest — a powerful reminder of why securing the best rate matters.

Fixed vs Variable Rate Mortgages

The UK mortgage market is dominated by fixed-rate deals, typically 2, 3, or 5 years. After the fixed period, borrowers revert to the lender's Standard Variable Rate (SVR) — usually significantly higher — unless they remortgage.

Fixed rate: Payment certainty for the deal term. You know exactly what you'll pay each month, which helps budgeting. You won't benefit if rates fall during your fixed period, and early repayment charges (ERCs) typically apply if you exit before the fix ends.

Tracker rate: Moves in line with the Bank of England base rate, usually at a margin above it (e.g. "base rate + 0.75%"). Payments fall when rates fall and rise when rates rise. Useful when you expect rates to fall or if you need flexibility — many trackers have no ERCs.

Discount rate: A percentage discount off the lender's SVR for a set period. Similar to a tracker but less predictable because SVR is set by the lender, not tied to Bank Rate.

LTV and How It Affects Your Rate

Loan-to-value is calculated as: LTV = (mortgage amount ÷ property value) × 100. A £200,000 mortgage on a £250,000 property is 80% LTV.

Lenders use LTV tiers to price risk. Lower LTV means lower risk to the lender (more equity cushion if you default), so rates step down at common thresholds: 95%, 90%, 85%, 80%, 75%, 70%, 65%, and 60% LTV. The best rates are typically reserved for borrowers below 60% LTV — often achieved through remortgaging after years of house price growth and capital repayment.

If your LTV has dropped since you took out your mortgage — whether through repayments, house price appreciation, or both — remortgaging could unlock a materially better rate.

Remortgaging — When and Why

Most mortgage holders should remortgage every 2–5 years when their current deal expires. Lapsing onto the SVR typically means paying 1.5–3% more than the best available deal — on a £200,000 balance that could be £3,000–£6,000 per year in unnecessary extra interest.

Start looking 3–6 months before your deal ends. Mortgage offers are typically valid for 3–6 months, so you can lock in a rate in advance without paying your current lender's ERC. Use a whole-of-market broker to compare all available deals — they have access to products not available directly to consumers.

You might also remortgage to: release equity for home improvements; consolidate unsecured debt (with care — you're converting unsecured debt to secured debt, which means your home is at risk if you can't repay); or switch from repayment to interest-only or vice versa.

Stamp Duty and Other Buying Costs

Mortgage payments are only part of the cost of buying a UK property. Budget for:

• Stamp Duty Land Tax (SDLT): In England and Northern Ireland, paid on purchase. First-time buyers pay 0% up to £425,000 on properties up to £625,000 (standard rates apply above). Standard rates: 0% up to £250,000, 5% on the portion from £250,001 to £925,000, 10% up to £1.5m, 12% above.
• Solicitor/conveyancer fees: Typically £1,000–£3,000 including searches, Land Registry fees, and bank transfer charges.
• Survey: A Level 2 HomeBuyer Report costs £400–£800; a Level 3 Building Survey £600–£1,500 for older or unusual properties.
• Mortgage arrangement fees: Many lenders charge £999–£2,000 to set up the mortgage. This can be added to the loan, but you'll pay interest on it for the full term.
• Buildings insurance: Required by mortgage lenders from exchange of contracts. Budget £150–£400 per year.
• Moving costs: Professional removals for a typical house cost £500–£2,000 depending on volume and distance.

In Scotland, Land and Buildings Transaction Tax (LBTT) applies instead of SDLT, and in Wales it's Land Transaction Tax (LTT) — both with different thresholds and rates.