About this calculator
Remortgage adverts compare two monthly payments and stop there. The honest comparison has three more ingredients: what it costs to leave (an early repayment charge of 1–5% of the balance if you are mid-fix, plus any exit fee), what it costs to arrive (product fee, valuation, legal work — though many remortgage deals bundle free legals and a free valuation), and the balance you still owe when the new fix ends. A switch that saves £160 a month but costs £5,000 in charges and leaves you owing more has not saved anything inside the fixed period.
This calculator therefore simulates both mortgages month by month across the fixed period you choose, then compares total cost: payments made, plus the balance still owed, plus every switching charge. That balance term matters — stretching the new term cuts the payment but leaves more debt outstanding, and counting the end balance stops a longer term from masquerading as a saving.
How to use it
- Enter your balance, current rate and remaining term from your mortgage statement.
- Set the ERC you would pay to leave today (0 if your fix has ended or you are on a tracker/SVR) and any exit fee.
- Enter the new deal: rate, term, fixed period, product fee, whether the fee is added to the loan, and any other switching costs.
- Read the net saving — positive means switching wins over the fixed period with all costs counted — and the break-even: how long payment savings alone take to cover the switching costs.
- Try the same new rate with the fee added to the loan, and with a longer fix, before deciding.
The formula
Counting the end balance as a cost is what makes the comparison fair across different terms: £1 of balance still owed is £1 you still have to repay later, exactly like £1 already paid out. The ERC is the current balance × your ERC percentage, matching how lenders charge it.
Worked example
You owe £200,000 at 5.50% with 20 years left — £1,375.77 a month. A new 2-year fix at 4.00% over the same term charges £1,211.96 — £163.81 a month less. But leaving costs a 2% ERC (£4,000) plus a £999 product fee: £4,999 of switching costs. Over the 2-year fix you pay £33,019 staying versus £29,087 switching, and you would owe £188,381 versus £186,399. Total cost: £221,399 staying, £220,485 switching — a true net saving of £914. On payment savings alone the switch breaks even in month 31, after this fix would already have ended; counting the lower balance is what puts it ahead inside the period.
Sources: Standard amortization mathematics applied to both deals; early repayment charge modelled as the percentage of the balance stated in typical UK mortgage offer documents. Last updated: October 2026.
Frequently asked questions
When does remortgaging actually pay?
When the rate gap is wide enough, and the balance large enough, for the monthly saving to outrun the switching costs within the fixed period. On a £200,000 balance each 1% of rate is worth roughly £110–£165 a month; on a £60,000 balance it is a third of that, and a £999 product fee can take years to earn back. Small balances often do better on fee-free deals even at a slightly higher rate.
Should I pay the early repayment charge to switch early?
Occasionally — if rates have fallen a long way and your ERC is in its final, cheapest year (many fixes taper: 5% down to 1%). Run this calculator with your real ERC: it counts the charge in full. More often the right answer is to wait for the deal to end, then switch ERC-free — and to start the application a few months ahead, because a remortgage offer is typically valid for up to 6 months.
Is it better to add the product fee to the loan?
It preserves your cash but you pay interest on the fee for the whole term — a £999 fee added to a 20-year loan at 4% costs about £1,214 in total. Paying upfront is cheaper if you have the cash; adding it is reasonable if the cash is your emergency fund or is earning more elsewhere. The calculator has a tick-box for exactly this comparison.
What happens if I do nothing when my fix ends?
You roll onto the lender's standard variable rate (SVR), historically several points above fix rates, with no ERC and full freedom to switch. The expensive option is usually staying on SVR by inertia — the comparison that matters then is SVR versus a new deal with zero ERC, which this calculator also runs: set the ERC to 0 and your current rate to the SVR.
What formula does this uk remortgage calculator use?
Both loans use M = P × r(1 + r)^n ÷ ((1 + r)^n − 1), simulated monthly over the fixed period. Total cost of a path = payments made in the period + balance still owed at the end + (for switching) ERC + exit fee + product fee + other fees. Net saving = total cost of staying − total cost of switching. Break-even = switching costs ÷ monthly payment difference. Counting the end balance as a cost is what makes the comparison fair across different terms: £1 of balance still owed is £1 you still have to repay later, exactly like £1 already paid out. The ERC is the current balance × your ERC percentage, matching how lenders charge it. The worked example on this page applies the formula step by step with real numbers, so you can verify the result by hand.