Mortgage Calculator — Payment, Total Interest and True Cost
Estimate your monthly house payment, total interest cost, and full repayment amount before you commit to a home loan. Adjust the home price, down payment, interest rate, and loan term to compare different scenarios side by side.
The Mortgage Payment Is Not the Cost of the House
The number a mortgage calculator returns covers principal and interest. It is the largest part of what you pay to own a home and it is nowhere near all of it, which is why buyers who budget against it alone find their first year uncomfortable.
| Cost | In the calculated payment? | Notes |
|---|---|---|
| Principal and interest | Yes | The figure this calculator produces |
| Property tax or council charges | No | Often collected alongside the mortgage, and it rises over time |
| Buildings insurance | No | Usually a lender requirement, not optional |
| Mortgage insurance | No | Commonly required below a certain deposit, and may fall away later |
| Service or ground charges | No | Applies to flats and managed developments |
| Maintenance and repairs | No | Irregular and unavoidable — the line renters never had to pay |
Maintenance is the one people leave out entirely, because it does not arrive as a monthly bill. It arrives as a boiler, a roof, or a rewiring, and setting aside a fixed amount each month is the only way to make it behave like the recurring cost it actually is.
When comparing owning against renting, the honest comparison is rent against every row of that table, not against the mortgage payment alone. Our guide on renting versus buying works through both sides.
Five Years In, You Have Barely Started
Long mortgages are dominated by interest at the beginning, and the scale of it surprises almost everyone.
Take 250,000 borrowed at 6% over thirty years. The monthly payment is about 1,499. Of the very first payment, 1,250 is interest and 249 reduces the balance — roughly 83% of it is the cost of the money rather than repayment of it.
| After | Total paid | Balance reduced by | Still owed |
|---|---|---|---|
| 5 years | about 89,933 | about 17,364 | about 232,636 |
| 10 years | about 179,866 | about 40,786 | about 209,214 |
A decade of payments totalling nearly 180,000 has cleared under 41,000 of debt. Nothing is wrong: interest is charged on the outstanding balance, and the balance starts at its maximum. But it explains why selling in the early years often returns less equity than owners expect, and why overpaying early is so much more effective than overpaying late.
Over the full thirty years this borrower repays about 539,595 against 250,000 borrowed — roughly 289,595 in interest, more than the house cost.
The Term Decision Is the Expensive One
Term affects total cost far more than most borrowers realise, because it changes both the payment and the number of times you make it.
| Term on 250,000 at 6% | Monthly payment | Total interest |
|---|---|---|
| 30 years | about 1,499 | about 289,595 |
| 15 years | about 2,110 | about 129,736 |
An extra 611 a month saves about 159,860 in interest. That is a genuine trade rather than an obvious win: the shorter term commits you to the higher payment permanently, with no option to drop back if circumstances change.
A middle path that many borrowers prefer is to take the longer term for the flexibility and overpay voluntarily when you can. You keep the right to pay the lower amount in a difficult year, and in good years you capture most of the interest saving. It requires the discipline to actually make the overpayments, which is the part that decides whether it works.
Fixed and Variable Are a Bet on Different Things
A fixed rate holds your payment steady for an agreed period. A variable rate moves with the market, up as well as down.
The choice is usually framed as predicting rates, which almost nobody does reliably. A more useful frame is what a rise would do to you. If a payment increase of a few hundred a month would be absorbed with mild annoyance, a variable rate is a reasonable risk. If it would break the budget, the fixed rate is buying certainty rather than chasing a forecast, and that is worth paying a small premium for regardless of what rates then do.
On a fixed deal, note when it ends. Reverting to a lender's standard rate at the end of a fixed period is a common cause of a sudden payment jump, and it is entirely avoidable by arranging the next deal before the current one expires.
How the Deposit Changes More Than the Loan Size
A larger deposit reduces the amount borrowed, which is the obvious effect. Three less obvious ones usually matter more.
- Lenders price by loan-to-value band, so crossing a threshold can move you into a materially better interest rate — sometimes worth more than the reduction in borrowing itself.
- Mortgage insurance is commonly required below a certain deposit and is a pure cost that buys the lender protection, not you.
- More initial equity means a fall in property values is less likely to leave you owing more than the property is worth, which is what constrains your ability to move or remortgage.
Against that, a deposit that empties your savings entirely is its own risk. Buying a house is immediately followed by needing money for it, and the worst time to have no accessible cash is the month after completion.
Before You Commit
- Add up every row of the first table, not just the calculated payment, and check that total against your take-home pay.
- Model the payment at a rate two or three points higher than today. If that version is unaffordable, the current one is only affordable for now.
- Budget the purchase costs separately — legal fees, surveys, taxes on purchase, moving. They are a lump sum, not a monthly one.
- Keep an accessible reserve after the deposit rather than putting every last amount into it.
- Check the early repayment terms before you sign, not when you first want to overpay.
To work out an honest purchase budget before looking at properties, our guide on how much house you can afford starts from income rather than from listings, and the loan calculator covers comparing offers where fees differ.