The group's data shows 11.40% of first home buyers on its books have a loan-to-value ratio (LVR) of 90% to 95%, while 33.8% have an LVR of 80-90%.
Lendi said cohorts who made use of the 5% deposit government first home home loan deposit scheme were most at risk and sensitive to interest rate rises.
This is because they borrowed higher amounts at higher LVRs and are now about to face much higher interest rates if they're rolling off a fixed rate, according to Lendi CEO Dave Hyman.
“For young Australians who took the Government’s First Home Buyers scheme the numbers are even more alarming, with more than half of those on an LVR above 95%, still on a fixed rate below 3%, leaving them exposed once their fixed term ends, with little room to move," Mr Hyman said.
For first home buyers who went through Lendi for their home loan, the average loan size is $557,000 - just below that of the wider owner occupier market, according to ABS data.
Those at or above 95% LVR who had fixed interest rates above 5% p.a. - 17% of the first home buyers on Lendi's books - had an average loan size of more than $814,000.
Lendi found the average first home buyer could save up to $568 per month or $6,825 over the year by switching to the lowest rate on its broker channel.
The data release comes as Westpac announced it would slash its serviceability buffer to 1% - lower than the APRA-defined 3% - for those who are refinancing to escape their mortgage prison.
However, this might provide little solitude for the near-half of first home buyers on Lendi's books who have LVRs of more than 80% who can't refinance.
Data from the regulator APRA shows among banks, $1.14 trillion mortgages are third-party originated i.e. through brokers - more than half of the total outstanding residential mortgage market.
“For those who do have a higher LVR and are finding it harder to refinance, a broker can look at your total income situation and debt to income ratio, to help you meet a lender's serviceability requirements," Mr Hyman said.
"With current credit cards, personal loans and car loans creeping higher, rolling this debt into a mortgage can help lower repayments, increase surplus income and may assist in keeping you out of mortgage prison."