Wait until you’re 33 to have kids if you want keep your salary: Study

It has been well-documented that working mothers have been often overlooked or penalized in the workplace, but a new study finds that the age at which a woman has her child also plays into the discrimination issue.

By the time they are 42, British women who had children before they were 33 earn 15 percent less than women without children, according to a report commissioned by the U.K.'s National Trade Union Congress (TUC).

However, women who have children after turning 33 actually experience a wage bonus of 12 percent over women who do not have children. This is explained by the fact that older mothers are more likely to return to their employers, reflecting that they are more established in their work place by the time they take leave.

On average, full-time working mothers witness a wage deduction of 11 percent compared to women who are working full-time without children.

The findings on parenthood, released Monday, also showed that overall motherhood is penalized while fatherhood is not.

Fathers who work full time earn on average 22 percent more than men without children working full time at the age 42. Fathers who have two or more children earn 9 percent more than fathers with just one child.

In fact, research cited by the TUC shows that internationally, fatherhood is viewed as more positive in job applicants than motherhood. Resumes from fathers scored more highly than identical ones from non-fathers, while the opposite effect was observed in women's applications. Mothers scored less highly than identical female candidates who did not mention parenthood.

A recent poll in the U.K. suggests that public opinion reflects this way of thinking. The Fawcett Society survey found that three in 10 think men are more committed to their job after having a baby – and nearly half of respondents think women are less committed after having children

The discrepancy between fathers' and mothers' wages seems to be because fathers who work full-time work an average half an hour longer a week than men without children. In contrast, mothers in full-time work, work about an hour less a week than women without children.

Overall, men in full-time employment still earn 34 percent more than women in similar full time working positions.

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