Minimum age and microchip rules for dogs entering the US

In short

• Your dog must be at least 6 months old on the day it arrives in the United States. This applies to every dog, from every country.
• Every dog needs a microchip that a universal scanner can read. CDC does not require a specific brand or the ISO standard.
• For dogs that have been in a high-risk country, the chip must be implanted before the rabies vaccination, or the vaccine does not count.
• Have your vet scan the chip before you travel. An unreadable chip can get a high-risk dog refused entry.

The minimum age on arrival

CDC sets one minimum age for all dogs entering the United States: 6 months old on the day of arrival. It does not matter where the dog comes from, whether it is a pet or a service dog, or whether it lives in the US.

What counts is the arrival date, not the booking date. A puppy that is five and a half months old when you buy the ticket is fine if it has reached the minimum age by the day it lands.

Airlines check too. CDC asks them to refuse dogs that appear to be under 6 months old. If your dog is small for its age, carry vet records showing its date of birth.

Why such a high age?

CDC does not give a reason for the exact number, but it fits the rabies vaccine timeline. A first rabies vaccine is only valid from 84 days (12 weeks) of age, and many documents also require a waiting period afterwards. A minimum age of 6 months leaves time for a dog to be vaccinated and protected before it travels.

The microchip: readable by a universal scanner

Every dog needs a microchip, a small electronic chip under the skin that stores an identification number. CDC uses it to link the dog to its form and documents.

CDC’s requirement is simple: the chip must be detectable with a universal scanner, a reader that picks up the common chip types. CDC says any brand is fine.

On the form:

• for a dog coming only from low-risk countries, the form does not ask for the microchip number, but the dog still needs a chip;
• for a dog that has been in a high-risk country, you enter the microchip number, and it must match the number on every vet document.

Does it need to be ISO?

CDC does not require the ISO 11784/11785 standard. Most chips used around the world follow it anyway.

CDC’s advice is practical: if your dog’s microchip number starts with a number other than 9, check with your vet that it can be read by a universal scanner.

Other countries may have stricter rules than CDC. If your dog will travel on from the US, or come back to Europe later, check those rules too: see returning to Europe with your dog.

High-risk dogs: chip first, vaccine second

For a dog that has been in a high-risk country in the last 6 months, the order matters. The microchip must be implanted before the rabies vaccination. CDC says that a vaccine given before the chip is not valid.

The reason: the chip is what proves that the vaccinated dog is the same dog that is traveling. A vaccine given before any chip was in place cannot be linked to the dog with certainty.

Check the dates on your vet records:

When a vaccination does not count, your dog starts again: a new vaccine given after the chip, then the waiting periods of its pathway (see US-vaccinated dogs and foreign-vaccinated dogs).

What to do if the chip is unreadable or missing

Before you travel

Ask your vet to scan your dog. It takes a minute. Check that the number on the scanner matches the number on your documents, digit by digit.

If the chip cannot be read

Chips sometimes fail or move under the skin. Your vet can try another scanner and scan the whole body. If it still cannot be read, your dog will need a new chip.

If your dog has no chip

Have one implanted by a vet. Ask for the chip number in writing, on the clinic’s records.

What a new chip changes

• Low-risk dogs: a new chip is enough. The form does not ask for the number.
• High-risk dogs: a new chip implanted after the rabies vaccine means that vaccine no longer meets the “chip first” rule. In practice, your dog needs a new rabies vaccination after the new chip, then new paperwork listing the new number. CDC does not publish a separate procedure for replacement chips, so plan for the full timeline and confirm with your vet.

If your dog has two chips

Some dogs end up with two chips, for example after a rescue. On the form, CDC asks you to enter the number that can be read and that appears on the vet paperwork. Your vet can help you check which one that is.

A quick checklist

1. Your dog will be at least 6 months old on arrival.
2. A vet has scanned the chip and the number matches your records.
3. For high-risk dogs: the chip date comes before the rabies vaccine date.
4. You carry proof of the date of birth if your dog looks young.

The rest of the form is explained in the CDC Dog Import Form, step by step.