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How old does a kitten have to be to fly?

Eight weeks, on every airline flying out of Portland. The number is the easy part. What actually stops a cat getting on a plane is almost never its age.

Search this and you'll get eight weeks, confidently, everywhere. That turns out to be right. I checked all six airlines operating domestic routes from PDX on 19 August 2026 and they agree, though United words it as two months and JetBlue doesn't publish a minimum age at all.

What each airline allows

Airline	Minimum age	Soft carrier, L x W x H	Cabin fee, each way
Alaska	8 weeks	17 x 11 x 9.5 in	$100
Delta	8 weeks	18 x 11 x 11 in	$150
American	8 weeks	18 x 11 x 11 in	$150
United	2 months	18 x 11 x 11 in	$150
Southwest	8 weeks	18 x 10.5 x 10 in	$125
JetBlue	Not published	17 x 12.5 x 8.5 in	$150

Read off each airline's own policy page on 19 August 2026 (Alaska, Delta, American, United, Southwest, JetBlue). These change without notice, so I reconfirm before booking rather than trusting this table or any other.

Alaska also requires the kitten to have been fully weaned and eating solid food, without nursing, for at least five days. That's a more useful test than the calendar, and it's the only one of the six that writes it down.

The carrier is what decides it

People assume there's a weight limit. There basically isn't. United states outright that there are no weight or breed limitations for pets in the cabin. Delta, Alaska, Southwest and JetBlue publish no figure. American has a twenty pound rule that applies only to the premium cabin on its three-cabin A321T, where they weigh the pet and carrier at check-in.

What every airline enforces instead is fit. American's wording is that the animal must be able to stand, turn, sit and lie down in a natural position without touching any side or the top. Delta asks that the pet can move around without touching or sticking out from the sides. So the question isn't how heavy she is. It's whether she can stand up inside the box.

Look at the Alaska row again. Nine and a half inches of height, against eleven on Delta, American and United. Alaska also bans hard-sided kennels in the cabin outright, so there's no swapping to a rigid carrier that holds its shape better. For a Portland business that matters more than any other line in the table, because Alaska flies roughly sixty-eight nonstops out of PDX and everyone else flies a handful.

Alaska is also explicit about what happens if you get it wrong: a pet that doesn't fit comfortably in its carrier or under the seat gets moved into a hard-sided kennel at your expense and checked into the baggage compartment. For me that isn't a downgrade, it's a cancelled trip, because I don't put cats in the hold.

Aircraft type moves the goalposts again inside a single airline. United caps carrier height at ten inches on the 737 MAX. American's regional Eagle jets take five pet carriers in the main cabin where mainline takes twenty across the whole aircraft. Size for the smallest plane on the itinerary, not the biggest.

Space runs out before the rules do

Every airline caps how many animals ride in the cabin, and the caps are small. Delta takes four in Main Cabin and two in First, none in Delta One. United takes four in economy and two in premium on most narrowbodies. Southwest reserves the right to limit a flight to six. Alaska doesn't publish a number at all and says the allotment varies by aircraft type, which means on the airline I use most I can't tell you in advance how full it is.

Delta still requires a phone call to add a pet. Alaska wants a chat or a call. That's part of why I ask for two days' notice, and why a same-week request costs more.

The destination state can set a higher minimum

Airline policy is a floor. Several states set their own minimum age for bringing in a cat, and a few set it above eight weeks. The rule that applies is the one for the state the kitten is arriving in, not the one it left. These change, so check with the destination state's department of agriculture before you book the vet.

Your own contract usually sets the highest one

Plenty of catteries won't release before twelve or fourteen weeks whatever the airline allows. CFA argues for sixteen weeks and won't let a kitten into a show hall younger than that, with twelve as the absolute floor, on the grounds that a kitten's immune system starts working independently at around twelve weeks.

Can two littermates share one carrier?

Sometimes, and it depends on the airline.

Alaska allows two pets of the same species and similar size in one carrier as long as nothing protrudes and neither is distressed. Delta allows two of the same breed and size between eight weeks and six months, charged as one pet. Southwest allows two small cats per carrier. United is the strict one: one pet per container, one container per ticketed passenger.

Because the fee is charged per carrier, two siblings going to the same city can work out much cheaper per kitten. Two kittens also fill a 17 by 11 by 9.5 inch box faster than one does, so I confirm the aircraft before I quote it that way.

What to do with this

• Eight weeks is the airline floor everywhere out of PDX. It is not a recommendation, and almost nobody who breeds cats seriously would place a kitten that young.
• Ask about the carrier before you ask about the age. On Alaska it's 17 by 11 by 9.5 and no hard sides.
• Check the airline operating each leg, not the one that sold the ticket, and recheck after any schedule change.
• Confirm the destination state's requirement for your route before you book the vet.
• Book early. Four pets per cabin fills up long before the plane does.