Over 750,000 18-to-23-year-olds have yet to claim their matured Child Trust Funds, according to HMRC.
The tax authority says that the accounts are worth £2,242 each on average.
Child Trust Funds are long term, tax-free savings accounts which were set up for children born between 1 September 2002 and 2 January 2011 with an initial government deposit of at least £250.
Young people can take control of their account at 16, but once the account holder turns 18 it matures, and they can decide whether they want to withdraw the money or re-invest it.
Young people can use the GOV.UK locator tool to find their Child Trust Fund quickly and for free. It requires the young person's National Insurance number and date of birth.
More than 563,000 young people went online to find their Child Trust Fund in the 12 months to the end of August 2025, says HMRC.
It takes about five minutes to submit a request to find a Child Trust Fund using the online tool and, for most, less than three weeks to hear back.
Angela MacDonald, HMRC's Second Permanent Secretary and Deputy Chief Executive, said:
'If you're between 18 and 23, you could be sat on a savings payout and not even realise it. Just search 'find my Child Trust Fund' on GOV.UK to find your savings account today.'
Internet link: HMRC press release