IF you have a 50p coin in your wallet or down the back of the sofa, you should dig it out because it could be worth a small fortune.

Rare coins with errors can be worth thousands of pounds each - but even coins in general circulation can be worth hundreds more than their face value.

4 Changechecker says the Kew Gardens design is the most sought after 50p coin

For instance, we found the most sought-after 50p coin, which is the Kew Gardens design, sold on eBay for up to £230.

In general, the rarer the coin - the more valuable it is, and experts at Changechecker.org have created a scarcity index that tracks circulating 50p coins.

The Kew Gardens 50p tops the index, with a mintage (the number of coins issued) of just 210,000, which means it is the rarest coin and is the most in demand.

Changechecker estimates that you can sell the coin for up to £120 on eBay, but a quick check on eBay shows a recently sold Kew Gardens 50p coin actually fetched nearly £230.

Another sold for £225 just this month.

Changechecker.org has created a scarcity index to help you work out how valuable your coin is

Collectors' editions of the coins and uncirculated ones are even more valuable, with some reaching prices of as much as £373.53 on the auction site.

The next 14 rarest coins are all from the 2012 Olympics, with the Flopsy Bunny coin from the Peter Rabbit collection coming in fifteenth.

An Olympic football 50p from general circulation can sell for up to £26, for example, while a collector's uncirculated version fetches up to £48.

Meanwhile, a triathlon design sells for up to £16.99; we found a Judo design that fetched about £20.99, a wrestling 50p for around £12.50, and a tennis version for up to £8.00.

Flopsy Bunny, which was lower down the list, still sold for £10.

How much are other 50p coins worth?

Many coins can be worth much more when sold on eBay as part of a collection.

Although sometimes you'll get better individual prices if another collector needs your coin to complete their collection.

Other coins sought after by collectors include the Beatrix Potter 50p coins.

These tend to go for less than £10 each but, the original 2016 Peter Rabbit coin did once sell for up to £840 on the auction website.

If you're looking to sell one today, you'd be lucky if you got that much.

4 The Kew Gardens coin could fetch over £200 on eBay Credit: Royal Mint

4 The 2012 Olympics Football 50p is worth up to around £26 on eBay Credit: Royal Mint

In the past, we've revealed the most valuable sought after coins after one seller pocketed £5,000 from flogging his Battle of Hasting's 50p.

Coins with mistakes tend to be among the highest values because of their extremely limited numbers.

A rare error coin from the 2012 Olympics set sold for £590 on eBay last August.

We've seen a similar coin listed that sold for over £10,000.

New coins that could be worth a mint too

In March last year, the Royal Mint re-released sets of five of the rarest and most popular 50ps to celebrate half a decade of the coin.

The new coins are made with old designs including Kew Gardens, Girl Guides and Scouts, but are stamped with the 2009 date which could make them super valuable among collectors.

The £90 collectors' proof sets sold out in February but you can still get uncirculated sets for £45 directly from the Royal Mint.

4 Uncirculated sets of the 2009 coins cost £45 directly from the Royal Mint

What makes a coin more valuable?

Generally, collectors look at the mintage figures of a coin to assess its value.

Rather than just basing a coin's value on the rarity, Changechecker.org looks at two other key pieces of information.

What do you do if you've got a rare coin? FIRSTLY, you need to make sure the coin is legit and not counterfeit. Around one in every four old £1 coins were thought to be fake, according to The Royal Mint, so there are probably more fakers in your spare change then you realise. The Royal Mint is unable to value a coin but it can confirm whether it is real or not. They will usually supply you with a letter to confirm this. Once you’ve found out whether the coin is real or not, you have a number of options – either selling it through a coin dealer, at auction or on eBay. You can look at eBay's recent sold prices to get an indicator of how much your coin usually goes for on the site.

This includes how many of each coin are listed as "collected" by members of the site, which indicates the relative ease of finding a particular coin.

The experts also track the number of times a design has been requested as a swap over the previous three months, showing the current level of collector demand.

While the index doesn't necessarily correspond to value, it is an effective indicator.

The Sun has also published a £1 scarcity index, so you can find out the value of each of the 24 £1 coin designs.

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We have also previously shown you which error coins can bag you the most dosh, including the 2012 London Olympics Aquatics 50p coin.

Last year, the Royal Mint launched a new Peter Rabbit coin which could be worth £840 as well as a Gruffalo coin.

Stephen Hawking fans have also been scrabbling to get their hands on a 50p coin celebrating his scientific work a year on from his death.

Royal Mint sparks coin hunt with 26 new 10p coins including 'ice-cream' and 'queuing'

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