Second-seat policies, explained
Verified June 11, 2026; every airline's page links the policy text itself.
Almost every "customer of size" policy is built on one physical test: can both armrests come down, and do you stay within them? If yes, you need one seat and at most an extender, and no policy applies to you. If not, airlines differ, a lot, in what happens next. Here's the landscape, in plain language.
The four models
- Buy-and-maybe-refund (US): you purchase a second seat up front, and get it refunded afterward if conditions are met. Alaska refunds if every flight in that direction departed with an open seat; Southwest refunds with three conditions (open seat on the flight, same fare class, claim within 90 days). This model rewards planning ahead.
- Buy-and-keep (most US carriers and Europe): the second seat is simply a purchase. American sells it at the same fare if booked together; Air France discounts it 25% and refunds it if the flight isn't full; KLM charges about 75% of the fare; Aer Lingus charges full fare; Lufthansa charges roughly the net fare and calls it, without irony, the "Free Neighbour Seat."
- One Person, One Fare (Canada, domestic): on Air Canada flights within Canada, qualifying passengers get the adjacent seat free: a regulator-ordered right, not a courtesy. It takes a medical form submitted at least 48 hours ahead, and it does not apply to international trips.
- No policy at all: JetBlue publishes no size policy, so an extra seat is just an optional purchase. That cuts both ways: nothing is required of you, and nothing is promised.
How refunds actually work
Where refunds exist, they hinge on details that are easy to miss in the moment:
- The empty-seat condition. Alaska, Southwest, and Air France refund only if the flight had room to spare, the logic being that your second seat didn't displace a paying passenger. On full flights, the refund evaporates.
- Same fare class. Buy both seats in the same fare class at the same time. A mismatch is the most common reason a Southwest-style refund is denied.
- The clock. Southwest gives you 90 days from travel to claim; Alaska also uses a 90-day window. Set a reminder for the week you get home.
- Get it in writing. Several airlines (American, Allegiant, Hawaiian, British Airways, United, Frontier) publish no refund terms for the extra seat at all. When you book by phone, ask the agent to note the refund terms on the record and email confirmation.
If you don't buy ahead and the airline decides you needed it
This is the scenario worth avoiding, and it's why the policies exist in writing: on most US carriers, if staff determine at the gate that you need a second seat and the flight is full, you will be rebooked on a later flight, and if it's determined after boarding, possibly deplaned for rebooking. Buying ahead (or on Air Canada domestic, filing the form ahead) converts an unpredictable airport conversation into a settled plan. The airlines' own pages say versions of the same thing; we just say it without the euphemisms.
What to do, practically
- Open your airline's page here and read the "Second-seat policy" section. It's the airline's actual rules, sourced, in plain English.
- If the armrest test is going to be close, price two seats at booking time. On airlines with refund conditions, that's often money you get back; at the gate, it's leverage you don't have.
- Book by phone where the policy requires it (American, Hawaiian, Lufthansa, British Airways) and say the airline's own policy name. Agents handle this regularly.
- Keep everything: booking confirmations, seat assignments, and the flight's load if you can see it. Refund claims are paperwork games; arrive with the paper.