Flying With a Baby on Frontier Airlines

Everything Frontier publishes, in one table

The second personal item is the whole story on this airline

Every airline on this site has some position on diaper bags. On most of them it is a footnote. On Frontier it is the difference between paying for a bag and not.

Frontier sells baggage as 1+1: every ticket includes one free personal item of up to 18 x 14 x 8 in and 35 lb, and the carry-on — 24 x 16 x 10 in, also 35 lb — is bought separately or comes with a bundle (flyfrontier.com bag options, read 2026-11-04). Against that backdrop, Frontier’s published rule that adults with lap infants may bring a second personal item, like a diaper bag, at no charge is not a courtesy. It is a free bag on an airline that charges for bags.

It is worth putting next to the opposite case. Alaska publishes that a diaper bag counts toward the ticketed adult’s standard carry-on limit and that lap infants get no allowance of their own, which is why our Alaska page is written around packing one bag rather than two. The two airlines have taken opposite positions on the same question, and there is no general rule to learn — only the airline you are actually flying.

The seat width rule, and why it probably rules out your car seat

This is the most useful number on any airline page we have written, and Frontier is the only carrier on this site that publishes it. Its car seat page states a minimum seat width of 17.4 in on A319 and A320 aircraft and 16.5 in on A321 aircraft (Frontier’s car seat FAQ, read 2026-11-04).

Most people never check, because most airlines never tell you. Here is what those numbers do to the car seats in our own registry:

Read that table and the conclusion is uncomfortable but simple: the cheap, light, aircraft-certified convertible seats that make sense for every other part of traveling with a baby are too wide for a Frontier seat on the airline’s own published numbers. If you are buying a car seat specifically to use on a Frontier flight, width is the first spec to check, not the last. Our travel car seats roundup ranks them on weight and certification; this is the one page on the site where width outranks both.

The second half of Frontier’s restriction is positional. A car seat must go in a window seat and is not allowed in exit or bulkhead rows. A lap infant separately cannot sit in a seat with an airbag seat belt, usually row 1. On Frontier, seat assignment is a paid extra — so these are rules you pay to comply with, and the time to do it is at booking. Using a car seat on a plane covers the mechanics once you are in the right seat.

Where Frontier sits against the airlines we have already read

The pattern across seven airline pages is that there is no pattern. Minimum ages run from none to 14 days with a letter. Diaper bags are free, charged, or counted against you depending entirely on the carrier. The only safe approach is the one this hub is built on: read the airline you are actually flying, on the day you book.

What to do before you book

Add the infant to the booking. Frontier publishes that a lap infant must be on the reservation and will receive a boarding pass (Frontier’s infant boarding pass FAQ, read 2026-11-04). Doing it later is a phone call you do not need.

Measure the diaper bag packed. The published box is 18 x 14 x 8 in including handles, wheels and straps. A soft bag that measures fine empty does not necessarily measure fine full. Our does a diaper bag count as a carry-on page is the general version of this question and small diaper bags for travel is the shortlist that measures under most personal item limits.

Measure the car seat at its widest point. 16.5 in is the number to beat if there is any chance of an A321. If your seat is wider, the choice is to check it free and hire or borrow at the other end, or to buy a narrow seat for flying.

Decide now whether the stroller gets gate-checked. Frontier allows both counter and gate checking and both are free. A compact fold can also go in the overhead bin, which is the one way a stroller never gets handled by anybody but you — strollers for overhead bins is the list of the ones that genuinely do, and gate checking a stroller covers what happens when the gate agent takes it anyway.

Carry age proof. Frontier publishes that a birth certificate may be requested. If your child is close to two, bring it — flying with a baby documents has the wider list.

The verdict on flying Frontier with a baby

Frontier publishes more usable detail than most legacy carriers do, and two of its rules are genuinely better than the competition: the second free personal item for a lap-infant adult, and free stroller and car seat checking that explicitly does not touch your allowances. On a 1+1 airline those are worth money, not goodwill.

The thing to plan around is the seat width. 17.4 in and 16.5 in are the numbers, they are published, and most car seats are wider than both. Check yours with a tape measure before you book a seat for your child, because the alternative is finding out at the end of a jet bridge.

The whole-trip version of all this is in our flying with a baby checklist, the ticketing question is answered properly at do babies need a ticket to fly, and if the carrier is coming with you, baby carriers through airport security covers the screening rules Frontier does not control. For the carrier itself, our Ergobaby vs Momcozy comparison is the budget-against-premium version of that decision — relevant if you are flying the cheapest airline and would rather not spend premium money on everything else. And once you land, the sleep problem starts: travel crib sheets is the small detail that catches people out in a hotel room at 10pm.