Mortgage calculator with overpayments and LTV
Enter the property price, your deposit, the interest rate and the term to get the monthly capital-and-interest payment, the loan-to-value ratio that decides which rates you qualify for, and the total interest over the life of the loan. Add a monthly overpayment to see how many years and how much interest it removes. No fees, taxes or insurance are assumed, so the figure is comparable between countries.
How to use the Mortgage Calculator
- Enter the price and your deposit, as a percentage or a cash sum.
- Enter the interest rate and the term in years.
- Add a monthly overpayment if you want to test one — leave it at zero otherwise.
- Press Calculate mortgage to see the payment, LTV, total interest and the saving from overpaying.
The payment formula
A repayment mortgage uses the same annuity formula as any level-payment loan:
M = P × i ÷ (1 − (1 + i)−n)
with P the amount borrowed, i the monthly rate (annual rate ÷ 12) and n the number of monthly payments. Worked example: a £300,000 property with a 10% deposit means borrowing £270,000. At 4.5% over 25 years, i = 0.00375 and n = 300, so M = 270,000 × 0.00375 ÷ (1 − 1.00375−300) = £1,500.75 a month. Over the full term that is £450,225 paid, of which £180,225 is interest — two thirds of the amount borrowed again.
Loan to value, and why it matters
LTV is the loan divided by the property price: £270,000 ÷ £300,000 = 90%. Lenders price in bands, and the difference between bands is real money. Dropping below 90%, 85%, 80%, 75% or 60% LTV typically moves you to a cheaper product, so if you are close to a threshold it is often worth finding a little more deposit or a slightly lower purchase price.
What overpaying does
Every extra pound goes straight off the capital, so it saves the interest that pound would have attracted for the rest of the term. On the example above, £100 a month extra clears the mortgage in 22 years 4 months instead of 25 years and saves roughly £22,100 in interest. The earlier you start, the bigger the effect — the same £100 a month in the final five years saves very little.
Check your lender's rules first. Many fixed-rate deals allow overpayments of up to 10% of the balance each year without penalty, and charge an early repayment fee above that. Some lenders reduce the term while others reduce the payment; only the first produces the saving shown here.
What is not included
| Excluded | Why |
|---|---|
| Product, valuation and legal fees | One-off costs that change the APRC, not the monthly payment |
| Buildings insurance, life cover | Required but priced separately |
| Property tax — council tax, US property tax | Local and highly variable; often escrowed in the US |
| Private mortgage insurance (US) and stamp duty (UK) | Jurisdiction-specific |
The calculation also assumes the rate holds for the whole term. In practice a UK mortgage is usually fixed for two to five years and then reverts, so treat the long-run total as an illustration of the maths rather than a forecast. An interest-only mortgage is different again: the monthly payment is simply balance × rate ÷ 12, and none of the capital is repaid.
Frequently asked questions
How much deposit do I need?
That depends on the lender, but rates improve in bands at 90%, 85%, 80%, 75% and 60% LTV. The calculator shows your LTV so you can see which side of a band you fall on.
Does this work for a US mortgage?
Yes. The capital-and-interest maths is identical. It excludes property tax, homeowners insurance and PMI, which are often bundled into a US monthly payment, so add those separately.
Is overpaying better than saving the money?
Compare the mortgage rate with the after-tax return you could get elsewhere, and check your early repayment charges. Overpaying is a guaranteed return equal to your mortgage rate.
Why is my lender’s figure slightly different?
Lenders vary in how they apply interest — daily, monthly or annually — and may round the payment up. Differences of a pound or two a month are normal.
Privacy
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Last updated 2026-09-23.