What decides how much a UK mortgage costs?
Three variables decide the cost — how much you borrow, the rate, and the term — and a small change in any one shifts your total by tens of thousands. A mortgage is likely the single largest financial commitment you'll make, and UK residential mortgages typically run 25 to 35 years. Lenders size the loan against your affordability, so it helps to know your monthly net income first — our UK salary calculator shows exactly what lands in your account after tax and National Insurance.
Most UK buyers choose a repayment mortgage, where each payment covers that month's interest plus a slice of capital, so the balance falls to zero and the home is yours. The alternative is an interest-only mortgage, where you pay only interest and must repay the capital separately at the end. Rates are driven by the Bank of England base rate (3.75% as of 2026-08-21) and lender swap rates, and are tiered by loan-to-value — a bigger deposit means a lower LTV and usually a better rate.
How are UK mortgage repayments calculated?
Every repayment mortgage payment uses the standard annuity formula, producing one constant payment for the whole term. Given a loan amount P, monthly rate r (annual ÷ 12), and total payments n (years × 12):
Monthly payment = P × r × (1+r)^n ÷ ((1+r)^n − 1)
In the early years most of each payment is interest, because the balance is large; as it falls, the interest shrinks and the principal share grows. This pattern is amortisation — the year-by-year split shown in the chart above.
Worked example: the calculator's default is a £280,000 home with a £56,000 deposit — a £224,000 mortgage at 4.5% over 25 years. That's a monthly payment of £1,245: in year 1 roughly £832 of each payment is interest and £413 is capital, and over the full term you pay £149,519 in interest (£373,519 repaid in total). By year 25 almost all of each payment clears the remaining balance.
Repayment or interest-only: which should you choose?
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 much do interest rates change your payments?
Even a 0.5% rate change shifts your payment and total interest significantly over a 25-year term. The table below shows monthly payments on a £200,000 mortgage across common rate levels:
| Rate | 20 yr term | 25 yr term | 30 yr term | Total interest (25 yr) |
|---|---|---|---|---|
| 3.0% | £1,109 | £948 | £843 | £84,400 |
| 3.5% | £1,160 | £1,001 | £898 | £100,300 |
| 4.0% | £1,212 | £1,056 | £955 | £116,800 |
| 4.5% | £1,265 | £1,111 | £1,013 | £133,300 |
| 5.0% | £1,320 | £1,169 | £1,074 | £150,700 |
| 5.5% | £1,376 | £1,228 | £1,136 | £168,400 |
| 6.0% | £1,433 | £1,289 | £1,199 | £186,700 |
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.
Should you pick a fixed or variable rate?
Fixed rates give payment certainty while variable rates can be cheaper but move with the base rate — most UK borrowers pick a 2- or 5-year fix. The 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.
Always compare mortgage deals using the APRC (Annual Percentage Rate of Charge), not just the headline rate. The APRC includes arrangement fees, which can make a nominally cheap deal more expensive overall.
How does LTV affect your mortgage rate?
Lower LTV means less risk to the lender and a lower rate, with the very best deals reserved for borrowers below 60% LTV. Loan-to-value is calculated as LTV = (mortgage amount ÷ property value) × 100 — so 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.
When and why should you remortgage?
Remortgage every 2–5 years when your current deal expires, ideally starting 3–6 months before it ends. Most mortgage holders should switch rather than lapse onto the SVR. 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.
What stamp duty and buying costs should you budget for?
Mortgage payments are only part of the cost — budget for stamp duty, legal fees, a survey, arrangement fees, insurance and removals. Since the thresholds reverted on 1 April 2025, the numbers to plan around (correct as of 2026-08-21) are:
- Stamp Duty Land Tax (SDLT): In England and Northern Ireland, paid on purchase. First-time buyers pay 0% up to £300,000 on properties up to £500,000 (standard rates apply above £500,000). Standard rates: 0% up to £125,000, 2% from £125,001 to £250,000, 5% from £250,001 to £925,000, 10% up to £1.5m, 12% above (gov.uk).
- 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.