Switch Mortgage Calculator — Product Transfer or Remortgage?

Most "switch" calculators are just remortgage calculators with a different heading. You enter one new rate, and they tell you what you'd save versus the standard variable rate. Fine — but that's not the decision most people are actually making.

When your fixed rate ends you have three options, not two:

A. Product transfer. Take the new deal your existing lender is offering. No affordability check, no valuation, no solicitor, often done online in a day. B. Remortgage. Move to a new lender entirely. Whole market, fresh application, valuation, legal work, four to eight weeks. C. Do nothing. Roll onto the SVR and pay for the privilege.

This tool prices all three on true cost over the deal period — every payment you'd make, plus the fees, minus any cashback, plus the balance you'd still owe at the end. It then tells you which routes you're even eligible for, because that changes the answer more often than the rate does.

If you're not sure whether to switch at all, start with the remortgage calculator instead. Come here once you've decided to switch and need to pick the route.

A product transfer — also called a product switch or rate switch — is when you move onto a new deal with the lender you already have. You're not borrowing more, you're not moving house, you're just repricing the same debt.

Because nothing about the loan changes, the lender doesn't need to reassess you. In practice that means: no affordability check, no credit check, no valuation, no solicitor, no legal fees. You can usually do it through online banking in minutes, and it completes the day your old deal ends. Most lenders let you reserve a rate three to six months early, and — this bit is underused — will let you cancel and re-reserve if rates fall before it starts.

The catch is simple and it costs people thousands: you only see one lender's deals. You have no way of knowing whether that rate is competitive without going and looking, which is precisely the effort the letter is designed to save you from making.

Post-2022, lenders got much better at retention. Product transfer rates today are often as good as what new customers are offered, and occasionally better. Sometimes. UK Finance forecasts product transfers will grow by around 13% in 2026 — a sign of how many people take the easy option without checking. The only way to find out is to check, and the difference between checking and not checking is usually a few thousand pounds.

Read that table again and notice what it's really saying. The product transfer column is a list of things you don't have to do. The remortgage column is a list of things you can do. Convenience versus optionality — and you pay for whichever one you pick.

Here's the mistake nearly every calculator makes: it compares two deals over the full remaining term — twenty-odd years. But you won't be on that rate for twenty years. You'll be on it for two, three or five, and then you'll do this all over again.

Compare over the deal period instead, and include four things:

That last term is the one everybody forgets, and it quietly flips results. A lower rate pays off more capital each month, so at the end of five years you owe less. Two deals with identical monthly payments can leave you with balances thousands of pounds apart. If you only compare monthly payments, you'll pick the wrong one and never know.

The calculator above does the full sum for all three routes, so you're comparing what actually lands in your pocket rather than what looks good on the letter.

4.38% with a £999 fee, or 4.65% with no fee? There is no universal answer, and anyone who gives you one is guessing. It depends entirely on the size of your mortgage.

A fee is a fixed cost. A rate saving is a percentage. So the bigger the balance, the more the rate saving is worth, and the easier the fee is to justify. Below a certain balance the fee-free deal wins; above it, the fee deal does. That balance is the crossover.

On a £185,000 balance over a 5-year deal, a £999 fee needs roughly a 0.11% rate saving to break even. Easy to clear. On a £60,000 balance it needs about 0.33% — much harder. Same fee, same deal, completely different verdict.

The calculator works out your exact crossover and tells you whether the fee is earning its keep. And if you're adding the fee to the loan rather than paying it upfront, remember you'll pay interest on it for the whole remaining term — which is worse than it looks.

Most lenders let you reserve a new deal three to six months before your current one ends, with no early repayment charge. Both routes work this way, so there's no reason to leave it late.

Leave your deal earlier than that window and you'll pay an early repayment charge — typically 1% to 5% of the balance, usually stepping down each year. Occasionally rates fall far enough that paying the ERC still wins; the calculator prices that in if you enter it.

The one thing you must not do is nothing. Roll onto the SVR — currently around 6.5%–7.5% — and you're paying two or three points more than you need to, on every pound you owe, for as long as you leave it. Around 800,000 UK homeowners a year accidentally do exactly this.

A useful habit: reserve a product transfer early as a floor, then shop the market properly. Most lenders will let you cancel it if you find better, so you've cost yourself nothing and protected yourself against rates rising in the meantime.

Tick the boxes in the calculator and it'll flag which routes are realistically open to you before you waste time on a route that ends in a decline. A rejected remortgage is not a free experiment — it leaves a mark on your credit file.

Since you took the mortgage out, two things have probably happened: you've paid capital off, and your home has (probably) risen in value. Both push your loan-to-value down — and LTV is the single biggest determinant of the rate you're offered.

The bands that matter are 60%, 75%, 85%, 90% and 95%. Cross below one and the rates on offer improve, typically by 0.15% to 0.30% per band. If you're at 76% LTV, a modest lump-sum overpayment to get under 75% before you apply can pay for itself many times over.

Check exactly where you sit with the house equity calculator, and if you're close to a band, the loan overpayment calculator shows what it would take to cross it.

You owe £185,000 on a home worth £300,000 — 62% LTV — with 21 years left. Your 4.9% fix is ending. Three options land on the table.

A — the letter from your lender

A product transfer at 4.65%, no fee. Two clicks, done by Friday.

B — what the market is actually offering

A 5-year fix at 4.38% with a £999 fee and £300 cashback, free legals and valuation. Six weeks of admin.

C — do nothing

The SVR at 7.1%. Around £350 a month more than either deal, immediately.

The verdict

The rate gap is only 0.27%, which sounds trivial. But on £185,000 over five years it's worth well over £2,000 — comfortably clearing the £999 fee, and that's before the £300 cashback. The remortgage wins by roughly £1,500, and you'll also owe slightly less at the end because the lower rate repays more capital.

Now change one thing. Your balance is £60,000, not £185,000. The same 0.27% saving is now worth about £810 over five years — less than the fee. The product transfer wins, and the two clicks were right all along. Same rates, opposite answer. That's why you run the numbers.

Official sources & further reading: read the remortgaging guidance at MoneyHelper, track the Bank of England base rate that drives SVRs, and verify any adviser on the FCA register. Browse every tool on the mortgage calculators homepage.