Mortgage rates have surged by more than half a percentage point this month, and if your fixed deal ends in 2026, that jump is heading straight for your monthly payment. According to Moneyfacts, the average mortgage rate climbed from 4.89% at the start of March to 5.50% by late March 2026, driven by geopolitical tension in the Middle East. For over one million homeowners whose deals expire in the coming months, that is a real and immediate problem.

What the numbers actually mean for your wallet

Let me run the numbers. On a £200,000 interest-only BTL (buy-to-let) mortgage, where you pay only the interest each month rather than reducing the loan balance, a rate of 4.89% costs £815 per month. At 5.50%, that rises to £917 per month. That is £102 extra every single month, or £1,224 over a year, on one property alone. Across a portfolio, those figures multiply fast.

The roughly 86% of borrowers currently locked into a fixed rate will not feel this yet. But for anyone whose deal ends between now and the end of 2026, the clock is ticking.

What the government and lenders are doing about it

Chancellor Rachel Reeves has moved to address the pressure. She brought together the six largest banks and building societies and secured a firm commitment. They will proactively contact 1.6 million customers whose fixed-rate deals end before the end of 2026. Lenders must lay out each customer's options, or explain how to access bespoke support, well before the payment changes.

She also reinforced the Mortgage Charter, a framework created during the mortgage crisis that gives borrowers specific protections. Under the Charter, lenders must offer options including a temporary switch to interest-only repayments for up to six months. The Charter also lets customers lock in a new rate up to six months ahead. They can switch to a new deal with their existing lender without a fresh affordability check or any impact to their credit score.

Nicholas Mendes, mortgage technical manager at John Charcol, welcomed the move but stressed it was not a new package of help. "It was more about giving people clearer notice, more time to plan, and a more obvious route into the support already available," he said.

What to do if your deal ends this year

The key window is six months out from your deal expiry. That is when lenders will let you lock in a rate, which means you can secure today's pricing even if rates move higher before your deal completes.

Mendes is direct on the approach. "The first step is to start early rather than waiting for the deal to expire," he said. "See what your existing lender will offer and compare that with the wider market. Work out what the payment looks like in pounds and pence, not just in headline rate terms."

He is clear that the focus should be on monthly affordability, not just the rate figure. A rate that looks manageable on paper can still put the squeeze on cash flow once you factor in all your other costs. His advice for anyone facing a difficult jump in payments is not to wait until the final weeks. Reviewing options early, understanding what the new monthly payment will be, and speaking to a broker or lender before pressure builds gives the best chance of finding a workable outcome.

If you are worried your new payment will be unmanageable, the Mortgage Charter options are there and your lender is now required to make them easy to access.