Stay-at-home mums and dads could be losing out on valuable pension money due to changes in child benefit rules.

Calculations by Royal London have estimated that women in particular may have lost out on more than half a billion pounds in state pension rights since the 2013 rule change.

Steve Webb, a former pensions minister and now policy director at Royal London, said: “a whole generation of women run the risk of getting reduced state pensions, reversing decades of progress.”

Under the current system, a parent receiving child benefit for a child under 12 will receive national insurance credits towards their state pension. Even if the main care-giver is not working and paying towards national insurance contributions themselves, their state pension record will be protected.

However, Royal London policy paper, Mothers Missing Out On Millions, argues the system is failing those affected by the high income child benefit tax charge.

Under the old rules, child benefit was paid at the same rate, regardless of household income. The January 2013 changes meant that families where one parent earns over £50,000 a year would incur a tax charge big – effectively wiping out their child benefit.

Due to this, many higher-earning household have stopped putting in a for claim child benefit. Unfortunately, this means that the stay-at-home parent will be losing out on their national insurance credits and putting their pension at risk.

To qualify for a full state pension, people usually need to have a minimum of 35 years of national insurance contributions or credits.

A Government spokesman said: “We have always been clear that families can submit the child benefit claim form to help protect their future right to the state pension.

“We provide specific information to all new parents and on gov.uk. If anyone is worried about their national insurance record, they can contact HMRC at any time to check how many years of credits and contributions they have built up.”

Want to put in a claim for child benefit? You can find more information at www.gov.uk/child-benefit/overview.