UK Mortgage Calculator

This calculator estimates your UK monthly repayment and loan-to-value ratio for both repayment and interest-only mortgages, and shows plainly why the lower interest-only payment leaves the full loan balance untouched at the end of the term.

For personal planning only — not financial advice.

Reviewed by CalculatorDrive Finance Editorial Board · Last updated

Loan Details

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Monthly Payment

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Total Interest

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Total Paid

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Amortization Schedule (First 10 Years)

Month Payment Principal Interest Balance
Run a calculation to view the schedule.

The short answer

A £350,000 property with a £70,000 deposit (20%, 80% LTV) leaves a £280,000 loan. As a repayment mortgage at 5.5% over 30 years, that's £1,589.81 a month and £292,331.31 in total interest — and the loan is fully cleared. As interest-only, the payment drops to £1,283.33, but total interest climbs to £462,000.00, and the full £280,000 is still owed at the end.

Key takeaways

  • £350,000 property, £70,000 deposit: 80% LTV, £280,000 loan.
  • Repayment at 5.5% over 30 years: £1,589.81/month, £292,331.31 total interest, loan fully repaid.
  • Interest-only at the same rate and term: £1,283.33/month (£306.48 less), but £462,000.00 in total interest and the full £280,000 principal still due at the end.
  • Stamp Duty, solicitor fees, and valuation costs are separate from the monthly repayment figure and need their own budget line.

Loan-to-value: why 80% is a common line

LTV = Loan Amount ÷ Property Price × 100

= £280,000 ÷ £350,000 × 100 = 80%

Lenders price mortgages in LTV bands, and 80% is a frequently used threshold — dropping below it (a bigger deposit) often unlocks noticeably better rates, since the lender's risk of loss in a repossession scenario is lower. Checking where a deposit lands relative to the nearest LTV band (75%, 80%, 90%) before finalizing it can be worth a small delay to save for a slightly larger deposit.

Repayment vs interest-only: the full picture

On the same £280,000 loan at 5.5% over 30 years, the two structures look close month to month but diverge sharply over the full term:

Repayment Interest-Only
Monthly payment£1,589.81£1,283.33
Total interest£292,331.31£462,000.00
Balance at end of term£0£280,000

Because the interest-only balance never shrinks, every single month's interest is charged on the full original £280,000 — not a declining balance — which is why total interest ends up £169,668.69 higher despite the lower monthly cost. Interest-only only makes sense with a credible, funded plan to repay that £280,000 separately, whether through investments, savings, or the eventual sale of the property.

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Frequently Asked Questions

What is the difference between repayment and interest-only mortgages?

A repayment mortgage pays down both interest and principal each month. On a £280,000 loan at 5.5% over 30 years, that is £1,589.81/month and £292,331.31 in total interest, and the loan is fully cleared at the end. Interest-only pays just £1,283.33/month but total interest is £462,000.00 — and the full £280,000 principal is still owed at the end.

What is loan-to-value (LTV) and why does it matter?

LTV is your mortgage amount divided by the property value, expressed as a percentage. A £350,000 property with a £70,000 deposit (20%) leaves a £280,000 loan, an 80% LTV. Lower LTV ratios generally access better interest rates.

How do UK fixed-rate mortgage terms work?

UK mortgages often have a fixed-rate period (e.g., two or five years) within a longer overall term (e.g., 25 years). After the fixed period, the rate typically reverts to the lender's standard variable rate unless you remortgage.

Are UK mortgage payments calculated the same as U.S. mortgages?

UK repayment mortgages use monthly compounding on the outstanding balance, which differs from the semi-annual compounding common in Canada and the monthly amortization approach in many U.S. calculators. Use a UK-specific tool for accurate estimates.

Does this calculator include stamp duty or solicitor fees?

No. Stamp Duty Land Tax, valuation fees, solicitor costs, and survey charges are significant UK homebuying expenses not included in the monthly repayment figure. Budget for these separately.

How do I use this UK mortgage calculator?

Enter property price in pounds, deposit amount, mortgage term in years, and interest rate. Select repayment or interest-only, then click Calculate to see your monthly repayment, total interest, and loan-to-value ratio.

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