Mortgage Repayment Calculator
Estimate your monthly payment and the total cost of a mortgage over its full term - on repayment or interest-only - and see what arrangement fees really add when they're rolled into the loan.
What this calculator tells you (and what it can't)
Give it the loan size, term, rate and any product fee, and it returns the monthly payment plus the total you'd hand over across the whole term. It's a ready-reckoner for comparing deals, not a quote: lenders round differently, charge interest daily rather than monthly, and your rate will change when the initial deal period ends. Always check the lender's own illustration before committing. Not sure what loan size to enter? Start with our borrowing power calculator to get a realistic figure from your income.
Mortgage pricing ultimately tracks the Bank of England base rate, so when you're stress-testing a deal it's worth glancing at where the base rate sits today and re-running the numbers a couple of points higher.
Repayment vs interest-only
On a repayment mortgage each monthly payment covers that month's interest plus a slice of the loan itself, so you owe nothing at the end. Early on, most of the payment is interest; the balance shifts as the debt shrinks. On interest-only, payments are much lower because they cover interest alone - but the entire original loan is still owed at the end of the term, and you need a credible plan (investments, sale of the property) to repay it. Lenders scrutinise that plan hard, and for good reason - the government-backed MoneyHelper service has impartial guidance on which structure suits which situation.
£220,000 over 25 years at 4.5%: a repayment mortgage costs about £1,223 a month, with roughly £147,000 of interest over the term. The same loan interest-only costs about £825 a month - but you'd still owe the full £220,000 in 2051.
The fee trap
A £999 arrangement fee looks small next to a £220,000 loan, and adding it to the mortgage feels painless. But rolled into a 25-year loan at 4.5%, that £999 quietly becomes roughly £1,670 by the time you've paid interest on it. Rule of thumb: pay fees upfront if you can, and when comparing two deals, weigh a lower rate with a big fee against a slightly higher rate with none - over a 2-year fix on a modest loan, the fee-free deal often wins. Use the "fee handling" toggle above to see both versions.
Term length: the quiet cost lever
Stretching the term cuts the monthly payment but inflates the total interest dramatically. £220,000 at 4.5% costs about £1,223/month over 25 years but £991/month over 35 - tempting, until you notice the 35-year version costs around £57,000 more in interest. If you take a long term for breathing room, check your deal allows overpayments so you can shorten it in practice - our overpayment calculator shows what that saves.
Frequently asked questions
How is a monthly mortgage payment calculated?
For a repayment mortgage the standard formula is M = P × r ÷ (1 - (1 + r)^-n), where P is the loan, r the monthly interest rate (annual rate ÷ 12) and n the number of months. For interest-only, it's simply P × r. This calculator applies exactly these formulas.
Should I add the arrangement fee to my mortgage?
Only if you can't pay it upfront. Adding it means paying interest on the fee for the entire term - a £999 fee can end up costing two thirds more over 25 years. If you do add it, overpaying by the fee amount early on undoes most of the damage.
Is a shorter mortgage term always better?
Shorter terms cost less in total interest but demand higher monthly payments, which reduces your flexibility if money gets tight. A pragmatic middle path is a longer term combined with regular overpayments - you get the lower total cost when you can afford it, without the contractual obligation.
Why is my lender's quoted payment slightly different?
Lenders calculate interest daily, round to the penny at different points, and may include insurance or account fees in the quoted figure. This tool uses the standard monthly amortisation formula, which is accurate to within a few pounds - fine for comparing deals, but always rely on the lender's formal illustration for the exact number.
What happens when my fixed rate ends?
You move onto the lender's standard variable rate (SVR), which is usually much higher. Most people remortgage to a new deal before that happens. Re-run this calculator with a pessimistic rate to stress-test what your payments could look like after the fix ends.