Southwest Pet Policy 2026: Fees, Carrier Size and How to Book

Travel · PetzDay Editorial · 2026-11-13

Southwest charges $125 each way for a cabin pet, caps soft-sided carriers at 18 × 10.5 × 10 inches, sells pet space by phone only, and never carries a pet in the hold.

Southwest is the second-cheapest of the five largest U.S. airlines for a cabin pet at $125 each way, and it is the most restrictive in one specific way: pet space is sold by phone only, and Southwest does not carry pets in the cargo hold at all. Buying a ticket does not reserve a pet.

This page covers the fee, the carrier dimensions that actually fit, the puppy rule, and the phone call you have to make.

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Southwest's 737 MAX 8 cabin. Pets ride under the seat in front of you, never on a seat. Photo: Ian Abbott / Wikimedia Commons (CC BY 4.0).

Southwest pet fee in 2026

• U.S. mainland: $125 each way, per carrier.
• Wholly within Hawaii: $35 each way.
• A round trip is two fees.
• The fee is charged per direction and paid when you add the pet to the reservation.

Southwest is cheaper than Delta, American and United ($150) and more expensive than Alaska ($100). The difference is small next to the booking constraint below.

Southwest carrier size: 18 × 10.5 × 10 inches

Southwest publishes a soft-sided maximum of 18 × 10.5 × 10 inches. That is the same length as Delta and American allow, but 1 inch shorter in height — which is exactly the dimension that decides whether a bag slides under the seat.

• Soft-sided only in practice. Southwest recommends soft-sided carriers, and the bag must fit under the seat in front of you.
• One carrier per ticketed passenger, with up to two same-species pets inside it — two small puppies of the same breed and size can share, two adult dogs cannot.
• The dog stays inside for the whole flight, including taxi, takeoff and landing.
• No exit row and no bulkhead — there is no seat ahead to stow under.

If you already own an 18 × 11 × 11 bag, it is one inch too tall for Southwest on paper. A 17 × 11 × 9.5 inch soft carrier clears every one of the five largest airlines, which is why the airline pet carrier size chart recommends that size.

Top-Side Expandable Pet Carrier, Treat Window,18x11x11 Airline Approved

18 in long matches Southwest, but check the height — its cap is 10 in, not 11

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How to book a pet on Southwest

This is the part people get wrong. Southwest pet space is limited and sold by phone only — you cannot add a pet during online checkout.

1. Book your ticket as normal, online or in the app.
2. Call Southwest and ask to add a pet to the reservation. Do this as soon as the ticket is booked; the per-flight pet limit is first-come, first-served.
3. Confirm the pet is on the reservation and keep the confirmation. A ticket alone is not a pet reservation.
4. Pay the $125 when the pet is added, or at check-in.
5. Check in at the counter so an agent can inspect the carrier.

Southwest sells cabin pet space by phone only, and there is no hold option behind it. Photo: Acroterion / Wikimedia Commons (CC BY-SA 4.0).

The puppy rule: 8 weeks, vaccinated, and one carrier

Southwest is the airline most likely to be asked about puppies, because its short-haul domestic network is where most first flights happen.

• Minimum age: 8 weeks, and the puppy must be fully weaned.
• Vaccinated pets only. Southwest is one of the few carriers that states a vaccination requirement for cabin pets; United, for comparison, does not require a rabies record for domestic cabin pets.
• Two puppies of the same species may share one carrier if they fit comfortably — a common question for a litter or a pair.
• The puppy still counts against the per-flight pet limit, which is why the phone call matters more than the fare.

What Southwest does not carry

• No pets in the cargo hold. Southwest sells cabin space only. A dog that does not fit under the seat cannot fly Southwest — there is no checked-pet or cargo fallback.
• No emotional support animals as pets. Under DOT rules, only trained service dogs fly free; everything else pays the pet fee and follows the cabin rules.

That last point is the reason Southwest is a poor choice for a medium or large dog. Alaska is the only one of the five that still sells hold space to ordinary passengers; the airline pet fee comparison lays out the alternatives.

Soft-sided, mesh on three sides, compressible — the shape Southwest expects under the seat. Photo: Sciencia58 / Wikimedia Commons (CC0).

Southwest domestic flights and paperwork

For a domestic cabin pet, Southwest asks for vaccination, not a health certificate. That is not the whole story:

• The destination state can require documentation — USDA APHIS lists state-by-state rules.
• International trips need an export certificate and the destination country's requirements, and Southwest's international network is limited.
• Returning to the U.S. always needs the CDC Dog Import Form receipt and a scannable microchip.

The health certificate and vaccine guide covers the documents in full.

FAQ

How much does Southwest charge for a pet?

$125 each way per carrier on U.S. mainland flights, and $35 each way for travel wholly within Hawaii. A round trip is two fees.

What size pet carrier does Southwest allow?

A soft-sided carrier up to 18 × 10.5 × 10 inches, and it must fit under the seat in front of you. That height cap — 10 inches — is one inch lower than Delta, American and United allow.

Can I add a pet to a Southwest reservation online?

No. Southwest sells cabin pet space by phone only, and space is limited per flight. Book the ticket, then call to add the pet before you buy a carrier.

How old does a puppy have to be to fly Southwest?

At least 8 weeks old and fully weaned, and Southwest requires that pets be vaccinated. Two puppies of the same species may travel in one carrier if they fit.

Does Southwest fly pets in cargo?

No. Southwest carries pets in the cabin only. A dog too large for an under-seat carrier cannot travel on Southwest at all.

Is Southwest pet-friendly compared with other airlines?

It is cheap ($125) and simple, but restrictive: phone-only booking, a 10-inch height cap and no hold option. Alaska is cheaper and more flexible; Delta, American and United cost more but allow taller carriers.

References

• Southwest Airlines — Pet policy
• Southwest Airlines — Optional travel charges
• Alaska Airlines — Pets in the baggage compartment
• USDA APHIS — Take a pet from one U.S. state to another
• CDC — Dog import form and instructions
• U.S. DOT — Flying with a pet

All web sources accessed November 13, 2026. Southwest's pet rules change without much notice; confirm on the phone when you reserve the pet.

Last reviewed: November 13, 2026.