Parents whose grown-up children have moved back to the family home could be paying an extra £17bn a year in living costs if they do not seek a contribution to rent or bills, Key Equity Release has found.

New research by the later-life mortgage adviser has analysed the true cost to parents of the so-called “boomerang generation”.

Office for National Statistics data shows that more than 3.8 million families in England and Wales comprise adults living with their parents – or around one in four households.

Overall 4.9 million adults live with their parents, suggesting some households have more than one grown-up sibling living in the family home.

Key estimates the additional cost of food and utilities at around £3,400 a year per household, which could total £17bn across all affected households if children make no contribution towards costs.

Parents aged between 54 and 62 are the most likely to have adult children living at home, potentially impacting their preparations for retirement.

Adult children living at home are more likely to be male, accounting for 61% compared with 39% female, while London has the highest proportion of affected families at 27%.

Nearly half (46%) of single-parent households have adult children living at home.

Key Equity Release chief executive Will Hale says: “Parents inevitably want to help out children and that is demonstrated by the numbers of adult children returning to live in the family home.

“Helping children can come at a cost however and parents need to consider their own financial situation.

“They are most likely to face the added financial costs of adult children living at home at a time in their lives when they are looking to pay off their mortgage and maximise pension saving for their own retirement.”

He adds: “As always, specialist advice is critical to ensure all appropriate options are considered and that any assistance provided for children does not compromise the customer’s own financial resilience.”