More than two million Premium Bonds prizes worth £79.4million remain unclaimed, according to the latest figures from National Savings and Investments (NS&I).
Premium Bonds are the most popular type of savings deal in the UK.
NS&I makes Premium Bonds payouts of between £25 and £1million every month, and normally these go out automatically.
But many of these prizes end up not being claimed.
This can happen if the original owner of the bond has died and NS&I has not been notified, or if you move house and fail to notify the savings institution.
Other common cases include where the person was given Premium Bonds as a child - which they later forgot about.
An unclaimed prize is defined as not paid to customer or cashed within 18 months of a draw.
There are 2.2million unclaimed Premium Bonds prizes, according to MoneySavingExpert.
The unclaimed prizes include five worth £100,000 and nine worth £50,000.
Some of these prizes date back decades.
MoneySavingExpert news and investigations editor Chris Newland said: “For those who suspect they might have let their Premium Bonds fall by the wayside, seeing these figures should be a wake-up call.
"Some of the eye-popping pots available could be potentially life-changing for people – especially right now."
How to track down Premium Bonds prizes
You can download a list of all unclaimed bond numbers here.
For recent prizes, you can check if you've missed out by visiting NS&I and using its online prize checker.
If you have lost the details of your account, want to register updated details, or want to notify NS&I of a bond-holder's death, you can telephone NS&I on 08085 007 007.
Website My Lost Account can also tell you if you hold any Premium Bonds which you may not have been aware of.
How do NS&I Premium Bonds work?
Each Premium Bond costs £1, and functions like a lottery ticket.
Savers earn no interest, but every bond is entered into a monthly prize draw where you can win between £25 and £1million tax free.
Each bond gives a separate chance to win.
Your chance of winning is completely down to chance - and you may not win anything at all.
Whenever you want to you can get all your money back from NS&I, though it may take a few days.
The minimum amount you can have invested in Premium Bonds is £25, and the maximum is £50,000.
At the moment the odds of a bond winning each month are 24,500 to 1 for every £1 Bond you have invested.
The vast majority of the prizes released each month are for £25.
Customers can choose to have their prizes paid straight into their bank account, or to have them automatically reinvested into new Premium Bonds.
