Remortgage true cost calculator

Net true cost is what switching costs, or saves, over your comparison period compared with staying where you are. It adds the ERC, plus fees after cashback, plus the difference in interest between the two paths. A positive figure means switching costs more than staying over that window. A negative figure means switching looks cheaper on the inputs you entered. A result near £0 is a tie, and then things like service, features and certainty matter more than the arithmetic.

Break-even is roughly how many months the lower monthly payment takes to repay the upfront cost (ERC plus net fees). If it runs past your comparison period, the switch has not paid for itself within that window. If it runs past the remaining term of the mortgage, switching does not pay back on the monthly saving at all. Any case for moving would then have to rest on something else, such as avoiding a reversion rate or needing a feature, not the rate gap.

Method

• Stay path: your balance at the current rate, repaid over the remaining term. Interest is summed month by month over the comparison period.
• Switch path: the new loan at the new rate over the new term, summed the same way. The new loan is your balance, plus every fee line if you choose to add fees to the loan.
• ERC: balance × the percentage, or the rate ÷ 12 × balance × the number of months, from what you type.
• Net true cost = ERC + fees − cashback + (switch interest − stay interest). Fees count in full whether you pay them upfront or add them to the loan. When they are added, the switch interest is on the larger loan, so the extra interest on the fees is included too.
• Break-even = (ERC + fees after cashback) ÷ monthly saving, rounded up to whole months. Adding fees to the loan raises the payment, so the saving shrinks or disappears.

EXAMPLE, fees paid upfront (the starter inputs): the ERC is £3,700 and fees after cashback are £1,249 (£1,499 − £250). Over 24 months the interest is about £15,080 if you stay at EXAMPLE 4.19% and about £14,897 at EXAMPLE 4.14%, so switching saves about £182. That gives £3,700 + £1,249 − £182 ≈ £4,767 net true cost, which is positive, so switching costs more. The monthly payment falls by only about £5 (£1,074 to £1,069), so break-even is about 988 months, or 82 years 4 months. That is far beyond the 22 years left on the mortgage. Set the ERC to None, as it would be once the fix ends, and the result is about £1,067 with break-even at about 20 years 10 months. That is still well beyond the 24-month window.

EXAMPLE: the £999 product fee added to the loan versus paid upfront

Same EXAMPLE house and the same EXAMPLE 4.14% over 22 years. Only the £999 product fee moves. The £500 legal fee is paid in cash in both columns, the £250 cashback is received in both, and the £3,700 ERC is paid on leaving in both.

Method: both columns are computed with this calculator's own logic (the Method list above: amortising payments, interest summed month by month over 24 months, net true cost = ERC + fees − cashback + interest difference). Source: our calculator methodology and MoneyHelper (below). Last checked 2 November 2026. EXAMPLE scenario rates, not a quote or advice.

Maths check: £3,700 + £500 + £999 − £250 + (£14,978 − £15,080) ≈ £4,847, against £3,700 + £1,249 + (£14,897 − £15,080) ≈ £4,767. The £80 gap is the interest on the added £999 over 24 months. Adding the fee keeps £999 in your pocket on completion. It costs about £80 over the 24-month horizon and about £525 over the full term, unless you overpay it off early without a charge.

What the calculator shows when you choose “Yes — add fees to loan”: it adds every fee line you enter. On the starters that is £1,499, so the loan becomes £186,499 and the payment about £1,077.46. Its net true cost then reads about £4,887: £3,700 + £1,249 + (about £15,018 − £15,080). That is about £121 more than the £4,767 for paying upfront, and the £121 is the 24-month interest on the added £1,499. To reproduce the £999 table above, enter legal as £0 and add the £500 yourself: the calculator gives about £4,347 added and £4,267 upfront, which is £4,847 and £4,767 once the £500 is included. Break-even shows “Not from payment saving alone” with fees added, because the payment is then higher than staying.

Source and check date

Payments use the standard amortising repayment formula, M = P × r(1+r)ⁿ ÷ ((1+r)ⁿ − 1), with r the annual rate ÷ 12 and n the term in months, as set out in our calculator methodology. The fee, cashback and ERC conventions follow MoneyHelper’s remortgaging guide, which also shows a fee added to the mortgage raising both the monthly payment and the total interest. The EXAMPLE rates are scenario rates. Last checked 2 November 2026.

What the number is not: it is not a quote, an offer or advice. It holds both rates constant, so it leaves out future rate changes and any reversion rate after your deal ends, unless you enter that as the current rate. It leaves out broker, valuation or exit fees you do not type in, any cashback clawback, and whether a lender will accept you. It compares interest only, not the small difference in balance left at the end. Lenders’ own interest calculations can differ slightly from this monthly method. A product transfer quote is a separate run in the remortgage vs product transfer calculator. For how the ERC line is built, see early repayment charges, and for timing see when to remortgage. This is not advice.