Fixed-rate cliff payment-shock calculator
When a fixed rate ends and you move to a higher rate, your monthly payment usually rises. This free calculator shows by how much: enter your balance, the years left, your current rate and the new rate, and it returns your new monthly payment, the monthly and annual increase, and the percentage change. It runs entirely in your browser, needs no email, and stores nothing.
Typical fixed rates, August 2026
The Bank of England's average rate on new 2-year fixed mortgages (75% loan to value) was 4.92%, and on 5-year fixed 4.78%, in August 2026. This is an average of rates actually charged that month, not a quote: what you are offered depends on your loan to value, fees and lender. Source: Bank of England, Interactive Database.
The "New rate" box below starts at this 2-year figure so you do not have to guess. Change it to the rate you are actually offered.
Work out your payment change
Free. No email needed. Runs in your browser.
Now
Monthly:
After your fix ends
Monthly:
Simplified illustration for a repayment mortgage. It assumes the new rate runs for the term shown and ignores fees, overpayments and future rate changes. Not advice. A regulated broker can confirm your real figures.
Why payment shock happens
If you fixed at a low rate a few years ago and now move to today's rates, the gap between the two rates shows up as a higher monthly payment on the same balance. The bigger the balance and the larger the rate jump, the bigger the shock. Seeing the number early, rather than on the first new direct debit, gives you time to plan. The fixed-rate cliff tracker sets out the wider picture.
Common questions
What does this calculator show?
It shows the difference between your current monthly payment and your new monthly payment when your fixed rate ends, based on your balance, remaining term, current rate and the new rate. It gives the monthly increase, the annual increase and the percentage change. It runs in your browser and stores nothing.
Is this advice?
No. It is an information tool to help you see the size of the change. It is not regulated mortgage advice. For a recommendation, a regulated mortgage broker can advise you.
What does it not account for?
It assumes a standard repayment mortgage and that the new rate runs for the term shown. It does not model interest-only mortgages, overpayments, fees added to the loan, or future rate changes. Treat the result as a guide.
My payment is jumping a lot. What should I do?
Do not leave it to chance. Arrange a new deal three to six months before your fix ends, and compare staying with your lender against remortgaging. The switch-or-stay tool helps you weigh the total cost of each.
Then weigh your options with should you switch or stay.
Founder, MortgageExplained
Adam spent over eight years as a mortgage adviser at Just Mortgages, with further experience in commercial finance. He is CeMAP and CF qualified. He built MortgageExplained to do one thing well: explain mortgages in plain English, so you know where you stand before you speak to a regulated broker. Every page on the site is written by Adam.
Figures checked: