If you haven't already checked your pockets or down the back of your sofa, it's probably time that you did.
Today the first day that the round one-pound coin is no longer legal tender.
Over the past six months, more than 1.2 billion round pound coins have been returned but some £500 million worth of the old coins are still in circulation.
They were replaced by the new 12-sided pound coin in March.
What is legal tender?
Legal tender is cash that must be accepted if offered in payment of a debt.
As the old pound coins are no longer legal tender, they can now be refused by businesses as payment.
But don't worry - many shops, banks and charities will still be accepting the coins for a short time.
Where can I spend my old one pound coins?
Poundland has said it will ignore the deadline and continue to accept old one pound coins in more than 850 of its stores until the end of the month.
Tesco also told ITV News:
Smaller shops have also been advised to continue accepting the round coins to provide a "useful community service" to customers.
What about banks?
Major banks have said that while they encourage customers to allow enough time to hand in their old coins, they will continue to accept deposits of round pounds from their customers after 15 October.
What has the Government said?
A spokesman for the Treasury said: