A recent report suggests mothers suffer pay penalty at work.

A study published by the Institute for Fiscal Studies shows that by the time a couple’s first child hits the age of 20, the mother earns around a third less than the father. This is likely a result of women working part-time in motherhood, the report revealed.

Before having children, women still earn less than men, but the gap increases after they have children. This is the case even when women have the same educational attainments as their male counter-parts.

As mothers spend more time in part-time employment than fathers, their likelihood of enjoying pay rises associated with more experience is slimmer.

About a quarter of the wage gap can be explained by the number of mothers, especially of young children, who work part-time and the resulting lack of pay progression.

Another ten percent of the pay gap is a consequence of the number of mothers who take time out of work altogether.

Sam Smethers, chief executive of the Fawcett Society, describes the issue as a “huge problem for the economy,” saying also that it should be possible for women who work part-time to be able to climb the career ladder.

IFS associate director Monica Costa Dias says that addressing this issue “would have the potential to narrow the gender pay significantly.”

This can be done through an increase in the number and quality of jobs that are open to part-time workers and by hiring flexibly, rather than only allowing existing employees to negotiate part-time work.

This month sees the celebration of the 100th anniversary since some women were allowed to vote. Despite this, the pay disparities that women face is unacceptable, said Dan Butler, Shadow Minster for Women and Equalities. He added that motherhood should not take a hit to women’s earnings.