Borrowers who reach the end of the five-year fixed rate this month could face a payment jump of £4,655 per year, based on the average mortgage rate.
Moneyfacts calculations show that borrowers who had taken out a five-year fixed rate in March 2021 could have locked in an average interest rate of 2.75%.
But now the average five-year deal has risen to 5.54%.
Based on a typical £250,000 mortgage with a 25-year repayment term, fixed interest costs have risen from £1,153 to £1,541 per month.
It means homeowners will have to find an extra £388 per month or £4,655 per year to meet the repayments.
The average two-year fixed rate is now even more expensive than five-year deals for the first time since last summer, the website said.
Moneyfactscompare.co.uk personal finance analyst Caitlyn Eastell says: “The outlook for interest rates has changed dramatically in recent weeks, spurred by unstable swap rates caused by the conflict in the Middle East.
“As a result, the mortgage market has been extremely volatile and more than 1,700 products have been withdrawn since March 9.
“While some of these deals have come back, they come at higher rates and it might be fair to assume that many lenders will follow this path, which could push average rates up further.
“Currently, lenders are expecting several increases in base rates, which could be demoralizing for borrowers.
“Even one 25 basis point increase could push mortgage rates higher, but borrowers on trackers will quickly feel the force of these increases.
“Approximately 1.8 million borrowers are expected to refinance this year; this includes those moving out of low five-year fixed rates.
“Borrowers typically have the option to renegotiate a new deal up to six months before their current interest rate expires. This could be critical for those concerned about rising costs.
“This also prevents borrowers from sliding towards their relapse rate, which would average more than £630 per month, an amount that many may not be able to afford.”