Mortgage repayment calculator

Enter what you’re borrowing, the interest rate and how long you’ll take to repay, and the calculator shows your scheduled monthly repayment, the total you’ll repay over the life of the loan, and the total interest that repayment adds up to. Add an optional overpayment and it shows how much interest you save and how much sooner you’re free of the loan.

How to use this calculator

The amount borrowed is the mortgage itself — the price of the home minus your deposit, not the price of the home. The interest rate is the annual rate your lender charges, entered as a percentage such as 4. The term in years is how long you have agreed to take to repay, most often between 20 and 35 years. The optional monthly overpayment is any extra amount you choose to pay on top of the scheduled repayment each month, which goes straight against what you owe.

Reading the results

The headline figure is your scheduled monthly repayment — the fixed amount you owe every month to clear the loan exactly on time. Below it, total repaid and total interest describe the whole life of the loan: total repaid is every monthly payment added together, and total interest is the part of that which is the cost of borrowing rather than the amount you borrowed.

The chart shows your balance falling over the term. It drops slowly at first and faster later, because early payments are mostly interest and only a little principal — a pattern called amortisation. As the balance shrinks, less of each payment goes on interest and more chips away at what you owe, so the curve steepens towards the end. When you add an overpayment, a second dashed line appears showing the faster path to zero.

The year-by-year table splits every year into interest and principal, so you can see the balance in any given year and watch the interest share fall as the principal share climbs.

A worked example

Take a €300,000 mortgage at 4% over 30 years. The scheduled monthly repayment is €1,432.25. Paid every month for 30 years, that adds up to €515,609 repaid in total — of which €215,609 is interest, more than two-thirds of the amount you originally borrowed.

The first year shows why the early curve is so shallow. Over year one you pay €17,187, but only €5,283 of it comes off the balance; the other €11,904 is interest — about 69% of the year’s payments. You end year one still owing €294,717 on a €300,000 loan. By the ten-year mark the balance has fallen to €236,352, and by twenty years to €141,463, with the pace quickening all the way down.

Overpayments change this sharply. On the same loan, paying an extra €100 a month saves €28,747 in interest and clears the mortgage 3 years 6 months early, in 26 years 6 months. Doubling the overpayment to €200 a month saves €50,412 and finishes 6 years 2 months early, in 23 years 10 months.

Assumptions and method

The calculator uses the standard annuity repayment formula — the same fixed-payment method behind almost every capital-and-interest mortgage. The annual rate is divided by 12 to give the monthly rate, the convention Irish lenders use, and that rate is held constant for the entire term. Real mortgages rarely behave that way: fixed rates re-fix after a few years and variable rates move, so the figure most lenders advertise as the true cost, the APRC, folds those changes and fees into a single yearly percentage.

The results ignore fees, mortgage protection insurance and any tax relief, so a real repayment schedule will differ. Overpayments are applied every month from month one; paying less regularly, or in lump sums, saves a different amount. This shows you the mechanism of a repayment — the trade-off between rate, term and overpayment — not a quote or an offer, and a mortgage adviser handles your own decision. Nothing you type is sent anywhere: every figure is worked out in your browser and never leaves it.