Why isn't my pet's microchip number 15 digits?

If you've just typed in a pet's microchip number and noticed it isn't 15 digits long, you might be wondering whether something has gone wrong. The good news is that it often hasn't. But it's always worth a second look, because a single wrong digit can make a big difference if that pet ever goes missing.

This guide explains what a standard UK microchip number looks like, why some numbers are different, and what to check before you save.

What a standard microchip number looks like

In England, the rules on microchipping cats and dogs are set out in The Microchipping of Cats and Dogs (England) Regulations 2023. These say a pet's microchip must have a unique number that includes the manufacturer's code, and must meet the international ISO standards for pet microchips.

Chips made to that standard carry a number that is exactly 15 digits long, made up of numbers only, with no letters or spaces. The first few digits usually identify the manufacturer or the country the chip comes from.

So if you're entering a number and it has 15 digits, that's what we'd expect to see for most pets chipped in the UK.

Not 15 digits? Don't panic

A microchip number that isn't 15 digits isn't automatically wrong.

The most common reason is that the chip was implanted outside the UK. Some countries use, or have used in the past, chips built to a different standard. These can be shorter (often 9 or 10 characters) and sometimes include letters as well as numbers. Rescue pets from abroad, and pets that have moved to the UK with their owners, quite often have chips like this.

That's completely normal, and you can still register the pet on Pet Database with the number exactly as it appears on the chip.

A heads-up about foreign chips and scanners

Even when a foreign chip is completely genuine, there's one practical thing worth knowing.

Most scanners used by UK vets, rescues and local authorities are designed around the standard 15-digit chips. Because a foreign chip is built to a different standard, some scanners may struggle to read it, or may not pick it up at all.

This isn't a legal rule, and there's nothing wrong with the chip itself. It's simply a helpful thing to be aware of. If you're a keeper with a pet who has a foreign chip, it's a good idea to:

• Let your vet know, so they can check their scanner reads it
• Keep the chip paperwork or pet passport somewhere safe and easy to find
• Ask your vet for advice on the best way to make sure your pet can always be identified

The typo risk

The other reason a number might not be 15 digits is much simpler: a digit has been missed, added or typed incorrectly.

Microchip numbers are long, and it's very easy to slip when copying one across, especially if you're working from a handwritten note or a busy day's paperwork.

Here's why it matters. The chip inside the pet will keep working perfectly. But if the number saved on Pet Database doesn't match the chip, the two won't connect. If the pet goes missing and is scanned by a vet, rescue or warden, they'll read the real number from the chip, search for it, and won't find the right owner. That's exactly the situation microchipping is meant to prevent.

A typo can also happen in a 15-digit number, so it's worth checking every number carefully.

Why getting it right matters

Under UK law, keepers must make sure their dog or cat is microchipped and registered on an approved database. According to GOV.UK, keepers can be fined up to £500 if their pet isn't microchipped or registered when it needs to be.

A record with the wrong number doesn't properly link the pet to its keeper, so it's important to make sure the number on file is the number on the chip.

How to double-check a microchip number

Before you confirm and save, take a moment to check the number against the chip itself or its official paperwork.

Check the source. The most reliable way is to scan the pet and compare the reading with what you've typed. If you can't scan, use the original chip paperwork, such as a microchip certificate, vet records or a pet passport. Pet insurance documents sometimes show the chip number too.

Read it back slowly. Go through the number in small chunks, for example three digits at a time, and compare each chunk carefully.

Count the characters. Make sure nothing has been missed or doubled up. This is where most mistakes happen.

Watch for lookalikes. If the number contains letters, check for easily confused characters, such as 0 and O, 1 and I, 5 and S, or 8 and B.

Copy rather than retype, if you can. If the number is in a digital record, copying and pasting it avoids mistakes altogether.

If you've checked and the number is correct, even if it isn't 15 digits, you're good to go.

A note for rescue teams

If you're registering a pet on someone else's behalf, you're often the first person to enter that chip number into a database. Getting it right at this stage saves the new keeper a lot of trouble later on, and gives the pet the best chance of getting home if they ever go missing.

If you see a warning that the number isn't 15 digits, it's not an error message. It's just a prompt to double-check before you save.

Quick recap

• Most UK microchip numbers are exactly 15 digits, numbers only
• A different length often just means a foreign chip, which is normal and can still be registered
• Some UK scanners may find foreign chips harder to read, so it's worth letting your vet know
• A typo means the pet can't be matched to their owner, even though the chip works fine
• Keepers can be fined up to £500 if their pet isn't properly microchipped and registered
• Always check the number against the chip or its paperwork before saving

For more on the wider rules, read our guide: Microchip Registration in the UK: What the Law Requires.

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