A cat microchip is a rice-grain-sized passive RFID tag implanted under the skin that returns one ID number when a scanner passes over it. That number is useless unless it is linked to your current phone number in a registry — which is the single most important thing to know about microchipping, and the reason most of the answers below come back to registration rather than the implant itself. The questions cat owners ask most in 2026 fall into five groups: whether it is legally required, whether it actually works, what the risks are, how to find and fix your registration, and what chip you need to travel. Each answer below is tied to the source that establishes it.
Table of Contents
- Is microchipping my cat required by law?
- Does a microchip actually get a lost cat home?
- What a microchip cannot do
- How risky is the implant?
- Finding and fixing your cat's registration
- Travelling abroad with a chipped cat
- Frequently Asked Questions
Is microchipping my cat required by law?
In England, yes. Microchipping has been mandatory for every cat over 20 weeks old since 10 June 2024, indoor-only cats included, and owners found without a chip get 21 days to have one implanted before facing a fine of up to £500, according to Defra's announcement on GOV.UK. The legal instrument is The Microchipping of Cats and Dogs (England) Regulations 2023, which extended the existing dog rules to cats. The implant alone does not satisfy the law.
GOV.UK's guidance on getting your dog or cat microchipped states that the keeper's contact details must be recorded and kept current on a government-approved database, and that failing to register carries the same penalty of up to £500. If you moved house or changed numbers and never updated the record, you are non-compliant even though your cat has a working chip. There is no equivalent nationwide requirement in the United States. Microchipping there is voluntary at the federal level, though shelters and rescues commonly chip animals before adoption as a condition of release.
Does a microchip actually get a lost cat home?
The strongest evidence comes from an Ohio State University study of more than 7,700 stray animals at 53 shelters across 23 states, published in JAVMA. Microchipped cats were returned to their owners 38.5% of the time, against 1.8% for cats with no chip — roughly a twentyfold difference. Read the first number carefully. It means that even among chipped cats, most were not reunited.
The researchers identified the main reason in their university news release: the registry held incorrect or missing owner contact information. The chip worked; the phone call went nowhere. That finding turns the practical advice on its head. The visit to implant the chip is a one-time, ten-minute job. Keeping the registry entry current is the ongoing task, and it is where the 38.5% figure is won or lost.
What a microchip cannot do
A microchip is a passive RFID tag. It has no battery and no GPS, so it cannot tell you where a wandering cat is — it only returns an ID number when someone physically scans the animal, as the AVMA's microchipping FAQ explains. That makes the chip a recovery tool, not a tracking tool. It works when a stranger picks up your cat and takes it to a vet clinic, shelter, or animal control officer with a scanner.
If nobody catches the cat, the chip never activates. Owners who want live location data need a separate GPS collar tag, which is a different device with a battery and a subscription. Frequency is the other technical wrinkle. The AVMA notes that US pet chips run at three frequencies — 134.2 kHz (the ISO 11784/11785 standard, 15 digits), 125 kHz, and less commonly 128 kHz — which is why clinics and shelters now use universal scanners that read all three. If your cat was chipped years ago, ask your vet to confirm the chip still reads on a universal scanner at the next checkup.
How risky is the implant?
Adverse reactions are rare and mostly minor. BSAVA's reporting scheme has logged 391 adverse reactions across more than 4 million microchipped animals since 1996, and the dominant problem is migration — the chip drifting from the implant site between the shoulder blades to the shoulder, leg, or chest, according to BSAVA's microchipping adverse reactions page. Migration rarely harms the cat but can cause a quick scan to miss the chip, which is another reason universal scanners and a full-body sweep matter.
Tumours at the implant site are the risk owners most often ask about, and the recorded numbers are very small: BSAVA logged two among 3.7 million animals on the Petlog database. Set that against a twentyfold improvement in the odds of getting a lost cat back. Signs worth a call to your vet after implantation are narrow and short-lived: swelling, discharge, or soreness at the site that does not settle within a day or two, or a chip you can feel sitting well away from where it went in.
Finding and fixing your cat's registration
If you have the number but no idea which registry holds it, start with AAHA's free Universal Pet Microchip Lookup. It accepts a 9-, 10-, or 15-digit number and names the participating registries the number appears in.
It is a pointer only — it holds no database of its own and cannot be used to register or update your details. Once it names the registry, you go to that company to make changes. A practical order of operations: If the lookup returns nothing, the chip may be registered with a company that does not participate, or it may never have been registered at all — common with chips implanted by a breeder or a shelter that expected the adopter to complete the step.
- Ask your vet to scan the cat and read out the number, then photograph the number on your phone.
- Run the number through the AAHA lookup to identify the registry.
- Log in to that registry and check the phone number and email, not just the address.
- Add a second contact — a partner, relative, or neighbour — so one dead phone line does not end the search.
- Re-check after every house move, phone change, or change of ownership.
Travelling abroad with a chipped cat
For travel from the US to the EU, order matters more than anything else. USDA APHIS states that cats must carry an ISO 11784/11785-compliant 15-digit chip implanted before the rabies vaccination, plus an EU-format health certificate endorsed by APHIS. A rabies shot given before the chip is not accepted.
The consequence is expensive and avoidable: if your cat was vaccinated first and chipped second, the vaccination has to be redone after the chip, with the waiting period restarting. Check the implant date against the vaccination date on your records before you book anything. The 15-digit ISO requirement also rules out older 125 kHz chips for EU entry. A cat carrying one needs an ISO chip implanted — or, where permitted, you must bring your own compatible scanner, which is a weaker plan than simply having the correct chip.
Frequently Asked Questions
Does an indoor-only cat in England still need a chip?
Yes. Defra's rules apply to every cat over 20 weeks old with no exemption for indoor cats.
Can I update my cat's details through the AAHA lookup tool?
No. AAHA's tool only names the registries a number appears in; changes must be made with the registry itself.
My cat's chip was not found on a quick scan — does that mean it failed?
Not necessarily. Migration is the most commonly reported issue, so ask for a full-body sweep with a universal scanner.
Will a microchip tell me where my missing cat is?
No. It is a passive tag with no battery or GPS and only returns an ID when someone scans the cat.