More than two million Premium Bonds prizes worth a combined £81million remain unclaimed, NS&I figures show.
Of the 2,324,683 prizes unclaimed, six are worth £100,000, according to figures obtained by Money Saving Expert (MSE).
There are also nine payouts of £50,000 yet to be claimed, and 14 prizes worth £25,000.
Helen Knapman, news and investigations editor at MoneySavingExpert.com, said: “Moved home over the years and not let NS&I know? Bought Premium Bonds prior to 2011 and not linked them to your bank account?
NS&I data shows that of the 2,324,683 Premium Bonds prizes unclaimed, six are worth £100,000
“These are just some of the reasons why you should check now if you’re due any missing Premium Bond prize wins.
“There are currently over two million prizes worth a combined £81million that haven’t been claimed for at least 18 months.
“That includes six prizes worth £100,000 – an astonishing amount for someone to be missing out on.
“If you’ve got Premium Bonds, you should also consider changing your settings to ensure any prize wins are always paid directly into your bank account or reinvested to ensure you don’t lose out in future.”
NS&I notifies Premium Bonds prize winners when they win a prize, but there are instances, such as if people move or change contact details without telling NS&I, when they don’t get the message.
This can lead to unclaimed prizes if the saver has opted to get the prize by cheque.
Savers can now opt to get prizes automatically paid into their bank account or reinvested into more Premium Bonds.
More than nine in ten prizes are now paid this way, however, there is still a wealth of unclaimed prizes from past draws.
Customers who think they may have unclaimed Premium Bonds prizes can check by using NS&I’s online prize checker or the prize checker app.
NS&I updates the prize checker tool each month, on the day after the first working day of the month.
Premium Bonds savers can check for unclaimed prizes via the NS&I website or prize checker app
To use the prize checker on the NS&I website, customers need their holder’s number.
This can be found on the Bond record or by logging into one’s account.
It has either nine or ten digits, or eight digits followed by a letter, NS&I explained.
If savers are using the prize checker app, they could also use their holder number.
People who have an NS&I number can only use this to check if they have won a prize on the prize checker app.
The NS&I number can be found on “most communications” they’ve had from NS&I – it’s 11 digits long and starts with an 11, 21, 31 or 41.