Most students will still be paying back loans from their university days in their 40s and 50s, and many will never clear the debt, research finds.
Almost three-quarters of graduates from England will have at least some of their loan written off, the study, commissioned by the Sutton Trust, says.
The trust says the 2012 student finance regime will leave people vulnerable at a time when family costs are at a peak.
Ministers said more students from less advantaged homes were taking up places.
The study, written by researchers at the Institute for Fiscal Studies (IFS), assessed the impact of the new student loan system for fees and maintenance, introduced in England from September 2012 to coincide with higher tuition costs of up to £9,000 a year.
The study - entitled Payback Time? - found that a typical student would now leave university with "much higher debts than before", averaging more than £44,000.
It says: "We estimate that students will leave university with nearly £20,000 more debt, on average, in 2014 prices (£44,035 under the new system compared with £24,754 under the old system).
"The vast majority of this increase is the result of higher fee loans to cover higher tuition fees."
In cash terms, the researchers estimate that graduates will now repay a total of £66,897 on average - equating to £35,446 in 2014 prices.
The report says the lowest-earning graduates - those whose salaries rarely go above £21,000 - will pay back less under the new regime, while those who earn higher salaries will pay back substantially more.
The decision to bring in a real, above-inflation interest rate on student loans means that almost half (45%) of graduates will pay back more than they borrowed in real terms.
However, even though large numbers of graduates will repay more than they borrowed, the vast majority will not return their loan in full, the study finds.
"We estimate that 73% will have some debt written off at the end of the repayment period, compared with 32% under the old system. The average amount written off will be substantial - about £30,000."
The researchers go on to say that, under the new system, most graduates will repay slightly less until they are in their mid-30s than they would have done under the old regime, but will then pay more in their 40s and early 50s.
The study cites the example of an "average" teacher, who takes out an average level of loan, works every year after graduating and has average earnings for the profession.
It says they would repay £25,000 in today's prices under the old system, finishing their repayments by the time they are around 40.
But under the new system, the same teacher would pay back around £42,000 in 2014 prices, but would not have finished paying back their loan by the time they are in their early 50s and would have around £25,000 written off.
Conor Ryan, director of research at the Sutton Trust, said: "There has been a lot said about the lower repayments that graduates make in their 20s under the new loan system, but very little about the fact that many graduates will face significant repayments through their 40s, whereas many would previously have repaid their loans by then.
"The new system will benefit graduates who earn very little in their lifetime. But for many professionals, such as teachers, this will mean having to find up to £2,500 extra a year to service loans at a time when their children are still at school, and family and mortgage costs are at their most pressing.
"With recent revelations about the proportion of loans unlikely to be repaid, it seems middle-income earners pay back a lot more but the Exchequer gains little in return. We believe that the government needs to look again at fees, loans and teaching grants to get a fairer balance."
Liam Byrne, the shadow minister for universities, science and skills, said: "Degree costs have trebled yet costs to the taxpayer have gone up, and now we learn our children and grandchildren will be paying off their student debt well into their fifties.
"The system has lost all fiscal credibility and is losing public confidence."
A spokeswoman for the Department for Business, Innovation & Skills said: "As a result of our reforms, a greater proportion of students from disadvantaged backgrounds are going to university than ever before.
"Most students will not pay upfront to study. There are more loans, grants and bursaries for those from poorer families.
"We have protected those on lower incomes by increasing the repayment threshold to £21,000 and our universities are now well funded for the long term."