The research found that the average gap in earnings between students from higher- and lower-income backgrounds is £8,000 ($11,338) a year for men and £5,300 ($7,512) a year for women, ten years after graduation.
Both were much better off than those who didn't attend or finish university at all - non-graduates are twice as likely to have no earnings as graduates 10 years on.
These two charts - from a more in-depth IFS report - show earnings of female and male graduates based on household income prior to university:
The gap between high income households (in green) and low income households (in red) increases the more both groups earn while the highest paid non-graduates earn similar amounts to graduates from low income households.
According to the report, the 10% highest-earning male graduates from richer backgrounds earned about 20% more than the 10% highest earners from relatively poorer backgrounds even after taking account of subject and the characteristics of the university attended.
Jack Britton, a research economist at the IFS and an author of the paper, said the findings show that backgrounds still mattered in the
"The advantages of coming from a high-income family persist for graduates right into the labour market at age 30. While this finding doesn't necessarily implicate either universities or firms, it is of crucial importance for policymakers trying to tackle social immobility."
Business Insider previously reported on the gender pay gap noted in the IFS report. It found that only one UK university - the London School of Economics - had more than 10% of female graduates earning over £100,000.