MOTHERS are being hit by a “pay penalty” if they work in part-time jobs, according to a new study.

Mothers tend to spend more time in part-time employment, so they do not benefit from pay rises associated with more experience, research found.

By the time a first child reaches the age of 20, mothers earn around 30 per cent less on average than similarly educated fathers, revealed a report funded by the Joseph Rowntree Foundation and published by the Institute of Financial Studies (IFS).

Some of the gap is explained by mothers in part-time jobs or taking a break from work altogether, said the report. The overall gender wage gap has fallen from 28 per cent to 18 per cent since the early 1990s for the less well educated, but has remained at 22 per cent for the highest educated, the study reveals.

Even before they have children, women earn around 10 per cent less than men, but the gap increases “rapidly” for many after they have children.

Monica Costa Dias, IFS associate director, said: “There are many likely reasons for persistent gaps in the wages of men and women which research is still investigating, but the fact that working part-time has a long-term depressing effect is an important contributing factor.

“It is remarkable that periods spent in part-time work lead to virtually no wage progression at all. It should be a priority for governments and others to understand the reasons for this.

“Addressing it would have the potential to narrow the gender wage gap significantly.”

Robert Joyce, IFS associate director, added: “It is now the highest-educated women whose wages are the furthest behind their male counterparts, and this is particularly related to the fact that they lose out so badly from working part-time.”

Sam Smethers, chief executive of the Fawcett Society, said: “What this study shows very clearly is that as a society we are not doing enough to value women’s talents. That is a blow to our productivity and a huge problem for the economy as a whole.

“We need to make it possible for part-time work to keep women on the career ladder. Employers should offer all roles, including more senior ones, as flexible working unless there is a good business case not to.”