Half of private tenants are paying more than 30% of their income on rent.
Only a quarter were found to have affordable rent spending less than 30% of their income on accommodation.
A report by housing charity Threshold, also found just over one-third expect to be renting for the next five years.
The majority don't want to be in the private rental sector, with 61% hoping to own their own home by 2028.
The research also found less than 1 in 5 feel secure in their rental accommodation and only 17% were renting by choice.
Threshold Chief Executive Officer, John-Mark McCafferty, says tenants are feeling less secure in their living situation.
"We've been doing this annual survey since 2018, and that's the highest figure in terms of feelings of insecurity with 48% of respondents stating that they feel insecure in their accommodation.
It's a steady year-on-year increase compared to last year when 44% of tenants said they felt insecure".