A staggering 57% of mortgage holders could not handle a $100 increase in their loan repayments, according to new research by Finder.com.au.This additional $100 is equivalent to an interest rate rise of just 0.45% based on the national average mortgage of $360,600. This means the average standard variable rate of 4.83% would only have to rise to 5.28% to put more than half of mortgage holders in stress.With increasing interest rates, some borrowers have little breathing room, said Bessie Hassan, money expert at Finder.com.au.“The typical mortgage holder will begin to struggle once interest rates reach around 5.28% – that’s a pretty small window before borrowing costs start to hurt,” she said.“The reality is borrowers have over-extended themselves if it only takes a $100 leap in repayments for more than half of homeowners to reach their tipping point.”Hassan expressed concern about mortgage holders and their exposure to mortgage stress, especially with rising rates forcing borrowers to use a greater percentage of income on their loans.Looking at higher rate rises, the research found 18% of borrowers could handle a monthly repayment increase of $250 while just 14% could manage $1,000 or more.There is a $209 monthly difference between the cheapest fixed interest rate (3.59%) and the most expensive (4.59%), Hassan said, meaning borrowers could be “throwing away thousands of dollars” per year.With the research also showing that 39% of all mortgages are interest-only, this highlights why the Reserve Bank of Australia ( RBA ) and the Australian Prudential Regulation Authority (APRA) have shown some concern, she added.Comparing genders, 63% of women and 50% of men would struggle to repay their mortgages with an increase of less than $100 per month.Across the states, South Australian borrowers were the worst placed with 70% saying they could not handle an increase of less than $100 per month. This figure was lower in New South Wales, Tasmania and Western Australia at 59% and further dropped to 51% in Victoria.