Old stamps without a barcode will not be allowed when posting letters from Tuesday August 1 2023.
Anyone using them could see their recipient charged for the postage if they want the item - with a standard first class letter costing £1.10.
It's even more for large letters which cost £1.60 first class and £1.15 second class.
Commemorative and Christmas stamps don't need to be exchanged and will still be valid for use at any time.
Royal Mail stopped the use of non-barcode stamps on January 31 2023, but gave a six-month grace period for people to use up their old ones.
Royal Mail says it introduced barcoded stamps in February 2022 to offer added security features, operational efficiencies and "exciting new services" through its app.
These will include the chance to scan the stamp QR code via its app so users can watch videos and send birthday recordings to each other.
How to swap old stamps
You can swap your old stamps for new barcode stamps directly with Royal Mail.
It hasn't given a deadline for when this needs to be done, so if you find some lurking at the back of a drawer at a later date you'll still be able to get an exchange.
The so-called Stamp Swap Out scheme sees customers pick up or print out a swap form, fill it in and post it off to Royal Mail with the old stamps inside.
If you have a printer you can print the form and send it addressed to: Freepost Swap Out.
Anyone with more than £200 worth of stamps must use a different form and send via a secure service. And if you don't have a printer you can request a form on Royal Mail's website, or pick one up from the Post Office. Information for bulk exchanges or those without a printer can be found here.
Which stamps are being barcoded?
- 1st Class
- 2nd Class
- 1st Class Large Letter
- 2nd Class Large Letter
- Christmas stamps (although old Christmas stamps without barcodes will still be valid after January 31 2023)
- International Tariff stamps
- Make up stamps (which are for specific values): 1p, 2p, 5p, 10p, 20p, 50p, £1, £2, £3, £5.
- Country definitive stamps: England, Northern Ireland, Scotland, Wales