⌂Free calculator

Mortgage calculator

See your monthly repayment, loan-to-value and total interest – then add a small monthly overpayment to see how many years and how much interest you could save.

Interest rate (per year)
Term
Monthly payment
—
Mortgage amount
Loan-to-value (LTV)
Total interest
Total cost
Overpaying saves

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How to use the mortgage calculator

  1. Enter the property price and your deposit (down payment). The calculator shows your deposit as a percentage.
  2. Set the interest rate and the term (typically 25–30 years in the UK and US, 20–30 years in Germany).
  3. Optionally enter a monthly overpayment. You will see the interest saved and how much sooner you would be mortgage-free.

How the repayment is calculated

A repayment (capital and interest) mortgage uses the standard annuity formula:

M = P × r × (1 + r)ⁿ ÷ ((1 + r)ⁿ − 1)

where P is the mortgage amount (price minus deposit), r is the monthly rate (yearly rate ÷ 12 ÷ 100) and n is the number of months.

Loan-to-value (LTV) = mortgage amount ÷ property price × 100

Lenders usually offer better rates at lower LTV bands, such as 60%, 75% and 85%. A bigger deposit can therefore lower both the amount you borrow and the rate you pay.

Worked example

A home costs 350,000 and you put down a 70,000 deposit (20%). You borrow 280,000 at 4.2% over 25 years.

  • r = 4.2 ÷ 12 ÷ 100 = 0.0035; n = 300
  • Monthly repayment ≈ 1,509
  • Total interest over 25 years ≈ 172,700
  • LTV = 280,000 ÷ 350,000 = 80%

If you overpay by 200 a month, you would clear the mortgage about 4 years and 8 months earlier and save roughly 36,000 in interest. Try it above with your own numbers.

Before you overpay

  • Many fixed-rate deals allow overpayments of up to 10% of the balance a year without a fee. Above that, early repayment charges may apply. In Germany, the allowance for Sondertilgung is set in the loan contract.
  • Keep an emergency fund first. Money paid into a mortgage is hard to get back out.
  • Compare the saving with what the money could earn elsewhere. Use our compound interest calculator to check.

Frequently asked questions

How much deposit do I need for a mortgage?
In the UK and US you can often buy with a 5–10% deposit, but rates are usually better from 15–25%. German banks often expect equity to cover at least the purchase costs (taxes, notary, agent), about 10–15% of the price.
Does the calculator include taxes and insurance?
No. It shows the capital and interest repayment only. Property tax, home insurance, mortgage insurance (PMI) and service charges come on top.
What happens when my fixed rate ends?
The rate changes to the lender’s variable rate or a new fixed deal, and the payment is recalculated on the remaining balance. Run the calculator again with the remaining balance as the price, a zero deposit and the new rate.
Is it better to overpay or invest?
Overpaying gives a guaranteed return equal to your mortgage rate. Investing may return more or less. Many people do a bit of both. For a personal recommendation, speak to a qualified adviser.

Last reviewed: November 13, 2026

Results are estimates for general information only and are not financial, tax, medical or legal advice. Check important figures with a qualified professional.