The Royal Mint has said that more than three percent of all pound coins in the UK are fakes.
The people who make all the UK's coins and banknotes have been looking at samples of the coins to see how big the problem is.
They've discovered that the number of fakes has doubled over the last 10 years and is increasing.
Some fakes are so good that machines can't spot them so banks can't always get rid of them.
How to spot a fake
It's thought there are as many as 44 million dodgy coins out there, but could you spot a fake one from a real one?
Some useful pointers include if the coin is brightly coloured, the writing is uneven or it has very smooth edges.
If you think you have a fake one, don't be tempted to spend it, instead take it to the bank and hand it in.