Check your pockets, piggy-banks and down the back of the couch now, folks.
A rare 50p coin featuring Sir Isaac Newton recently sold on eBay for £120 (240 times its value) - and you could have one worth £245 in your spare change without even knowing it.
That's right, it's worth checking the design of any 50p coins you have to see if it could be one of the rarest and most valuable ones in circulation.
While the most sought-after 50p - the Kew Gardens design - can fetch up to £245 on the likes of eBay, other rare 50p coins usually achieve a premium of around 10 to 12 times face value (£5-£6) when they are sold on.
It goes without saying, perhaps, but the rarer the coin the more it's worth, and experts at Changechecker.org have created a scarcity index that tracks which circulating 50p coins are the most scarce and collectable.
The index uses a unique combination of mintage, collecting and swap data to give the most up-to-date picture of today’s 50p coin collecting market.
The aforementioned Kew Gardens 50p tops the scarcity list. With a mintage (the number of coins issued) of just 210,000 it is the rarest coin and, therefore, the most in-demand.
The next nine scarcest coins are all from the 2012 Olympics.
Football, Triathlon, Judo, Wrestling 50 pences will sell for between £8 and £21 on eBay or up to £33 for a set of four.
If you discover you have a rare 50p, you can either choose to sell the coin on eBay or through a specialist like ChangeChecker.org.