The federal government is expected to ditch one of its most controversial budget measures - the plan to apply real interest rate to student debts - following advice from the architect of the HECS repayment scheme that it is unfair to poor graduates.

Detailed modelling by leading education economist Bruce Chapman has found poor graduates could pay 30 per cent more for a degree than their high-income counterparts if the government indexes student debts at the government bond rate rather than inflation.

Poorer graduates would pay significantly more than their rich counterparts for their degrees under the government's plans to charge higher interest on university degrees. Credit:Louise Kennerley

Women who take time off work to have children would be among the hardest hit.