What it is
A cat microchip is a passive radio-frequency identification (RFID) transponder roughly the size of a grain of rice. It is implanted with a needle between the shoulder blades and remains in place for the cat's lifetime. The chip itself stores only a 15-digit ISO 11784/11785 number — no GPS, no health data, no personal information.
That number is linked to the owner's contact details, the cat's description, and the implanting vet's details on a separate registration database. A scanner held near the cat reads the chip's signal passively — without any battery or power source in the chip — and displays the number. The holder can then search that number on the relevant database to find the owner.
Why it matters
Microchipping is the most reliable way to permanently identify a cat and reunite it with its owner after loss. Collars and tags can fall off; a microchip cannot. Since June 2024, microchipping all owned cats in England is a legal requirement. The law and its enforcement process are explained in our news article on the cat microchipping law update.
A chip is only useful if it is registered correctly. A cat with a chip registered on a database the finder does not search — or with outdated contact details — can still end up unreturned. Use Check-a-Chip to confirm your cat's chip is registered and up to date.
The implant procedure
The chip is implanted by a trained implanter — usually a vet or vet nurse — using a sterile needle. The procedure is brief, requires no anaesthetic, and is typically done at the same appointment as the first kitten vaccination. See our cat vaccinations guide for timing information.
Registration databases
In England, chips must be registered on one of Defra's approved databases. The most commonly used include:
- Petlog (run by the Kennel Club)
- Identibase
- PetDatabase
- Anibase
The Check-a-Chip service searches across all approved databases simultaneously using a chip number.