The pre-flight checklist
Everything to do in the four weeks before you fly with a pet, in the order you have to do it. Every number here was read on the airline’s own policy page. Where an airline does not publish something, we say so instead of filling the gap.
The one thing people get wrong. They buy the carrier first and check the airline second. Every airline publishes a different maximum for the space under the seat, and no airline “approves” carriers — they publish a limit and the gate agent decides whether your bag fits it. Book the pet’s place first, then buy to that number.
Four weeks out — book the pet, not just the seat
Most airlines cap how many animals travel in the cabin per flight, and it is first come, first served. Your ticket does not reserve your pet a place. This is the step that runs out.
| Airline | How to book the pet | Places per flight | Fee |
|---|---|---|---|
| American Airlines Minimum age 8 weeks | Add the pet to your booking on the website or the app. | Up to 20 carriers across all cabins on mainline aircraft. Regional aircraft carry between 1 and 5. | $150 each way, per carrier |
| Delta Minimum age 8 weeks | You have to call Delta Reservations. Have the carrier dimensions ready when you do. | Four in the main cabin, two in first. First come, first served. | $150 each way, per carrier |
| United Minimum age 2 months domestic, 6 months international | Add the pet when you book, or call. Cats, dogs and rabbits only. | Space-controlled per flight and per aircraft type. Some narrowbodies allow one pet per passenger. | $150 each way, per carrier |
| Alaska / Hawaiian Minimum age 8 weeks | Add the pet when you book, or call. | Space-controlled per flight. Book early. | $100 each way, per carrier ($35 within Hawaii) |
| JetBlue Minimum age 8 weeks | Add the pet when you book. Cats and dogs only. | Space-controlled per flight. | $125 each way, per carrier |
| Southwest Minimum age 8 weeks | Southwest recommends calling to reserve, because space is limited. | Space is limited and not guaranteed. Southwest recommends booking by phone. | $125 each way, per carrier |
| Frontier Minimum age 8 weeks | Pay in advance during booking. | Space-controlled per flight. | $99 each way, per carrier |
| Allegiant Minimum age 8 weeks | Add the pet when you book. | Space-controlled per flight. | $50 per segment, per carrier |
| Breeze Minimum age 8 weeks | Add the pet when you book. | Five pets per flight. | Not published — the charge appears at booking |
Two airlines want a phone call rather than a form: Delta takes pet bookings by phone, and Southwest recommends calling because space is limited. Have your carrier’s three measurements written down before you dial — they will ask.
Three weeks out — measure your pet, then buy the bag
Measure lying down
Nose to the base of the tail, then add 2 inches. That is the interior length your pet needs to lie flat for the whole flight.
Measure standing up
Floor to the top of the head. Your pet has to be able to stand and turn around inside. That is the rule every airline writes, and the one agents actually check.
Then check the airline
Compare the carrier’s exterior length, width and height against your airline’s published limit. Interior is always smaller than exterior.
Between two sizes, take the bigger interior — but only if that bag’s exterior still clears your airline. The space under the seat does not negotiate. How to measure, step by step · All nine limits side by side
Three to one weeks out — get the carrier to stop being a carrier
A cat that meets the bag for the first time at the airport will fight it. Two weeks turns it into furniture. This is the part people skip and then regret at security.
Days 1–4
Open the bag, take the door off if it comes off, and leave it in the room where they sleep. Do not put them in it. Put treats near it, then inside it.
Days 5–10
Feed them in it. Then close the door for a minute while they eat, and open it before they ask. Build up to ten minutes.
Days 11–14
Pick the bag up and walk around the house. Then a car trip that ends somewhere good, not at the vet. Movement is the part they have to get used to.
Put something that smells of you in there, and leave it there. Wash it after the trip, not before.
One week out — the paperwork and the re-check
Requirements for domestic flights inside the United States vary by airline and by the state you are landing in. Some ask for a health certificate from a vet, some do not, and a few states have their own rules regardless of the airline. We are not going to publish a number here that might be wrong for your route: open your airline’s own policy page and read the paperwork section, and if a certificate is needed, book the vet now, because most are only valid for a limited window before departure.
| Airline | Does the carrier count as your bag? | Official policy |
|---|---|---|
| American Airlines | The carrier replaces your carry-on bag or your personal item. | Read it |
| Delta | The carrier must fit fully under the seat in front of you. | Read it |
| United | The carrier counts as your carry-on allowance. | Read it |
| Alaska / Hawaiian | The carrier counts as your carry-on allowance. | Read it |
| JetBlue | The carrier and pet count as one personal item. | Read it |
| Southwest | The carrier counts toward your carry-on allowance. | Read it |
| Frontier | The carrier counts as your carry-on. A personal item or a bag costs extra on top. | Read it |
| Allegiant | The carrier counts as one of your two carry-on items. | Read it |
| Breeze | The carrier counts as a carry-on item. | Read it |
While you are on that page, check the published size again. Airlines change these without announcing it, and the limit that matters is the one on the day you fly.
The day before
Trim their nails
Claws catch in mesh, and a pet hooked into the side of the bag at the security line is a bad thirty seconds for everyone.
Ask your vet about sedation
Do not sedate on your own initiative. Sedatives affect breathing and temperature regulation, and altitude changes how they act. If you think your pet needs something, that is a conversation with your vet, not a decision to make the night before.
Plan food and water
Ask your vet how long before the flight to stop food for your particular animal. Freeze a little water in the bowl so it melts slowly instead of spilling on the way.
At the airport — the thirty seconds nobody warns you about
Your carrier goes through the X-ray machine. Your pet does not. You take them out and carry them through the metal detector in your arms, in a queue, in socks, with your bags going away from you on a belt.
That is the moment animals are lost in terminals. Put a harness and lead on your pet before you leave home, under your control the whole way through. A collar is not enough — a frightened cat reverses out of a collar in one movement.
- Harness on at home. Lead clipped and in your hand before you join the queue.
- At the belt, take the pet out and put the empty carrier on the X-ray.
- Carry them through the detector. Keep the lead short and wrapped once around your hand.
- Back in the bag on the other side, before you pick anything else up.
- Ask for a private screening room if you are travelling alone with a nervous animal. They exist and you are allowed to ask.
At the gate, the bag goes fully under the seat in front of you for the whole flight. It does not go on your lap, on the seat, or in the overhead.