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For a repayment mortgage, the monthly payment is M = L × r ÷ (1 − (1 + r)^−n), where L is the loan, r is the monthly interest rate and n is the number of months. For example, £240,000 over 25 years at 4.5% costs about £1,334.00 a month.

With a repayment mortgage, each payment covers interest and part of the loan, so you owe nothing at the end. With interest-only, you only pay the interest, so payments are lower but the full loan is still owed at the end. On £240,000 at 4.5%, that's about £900 a month instead of £1,334, with £240,000 left to repay after 25 years.

Overpaying cuts the loan faster, so you pay less interest. On £240,000 over 25 years at 4.5%, an extra £100 a month clears it about 3 years early and saves around £21,746 in interest. Many lenders limit overpayments to 10% of the balance a year during a fixed deal, so check before overpaying.

Loan to value is the size of your mortgage as a percentage of the property price. A £240,000 loan on a £300,000 home is 80% LTV. Lenders usually offer better rates at lower LTVs, often in bands such as 60%, 75%, 85%, 90% and 95%.

A shorter term means higher monthly payments but much less interest overall. £240,000 at 4.5% over 20 years costs about £1,518 a month and £124,406 in interest, against £1,334 a month and £160,199 over 25 years.

It assumes one interest rate for the whole term. In practice most UK mortgages start on a fixed or tracker deal and move to the lender's standard variable rate afterwards, unless you remortgage. It also leaves out arrangement fees, stamp duty, legal costs and insurance.

For a repayment mortgage the monthly payment is M = L × r ÷ (1 − (1 + r)^−n), where L is the loan (price minus deposit), r is the yearly rate divided by 12 and n is the number of months. Each month, interest is charged on the balance still owed and the rest of the payment reduces the loan. For interest-only, the payment is just the interest and the loan is still owed at the end.

Any overpayment is taken off the balance each month on top of the normal payment. The payment stays the same, so the mortgage is cleared sooner and less interest is charged. "Interest saved" compares this with no overpayments.

It uses one rate for the whole term, whereas most UK mortgages start on a fixed or tracker deal and move to a different rate afterwards. It leaves out arrangement fees, stamp duty, legal costs, insurance and any early repayment charges.