On US domestic flights, a child under 2 can fly free on your lap—no ticket, no fee. That's the cheapest option, but a paid seat with an FAA-approved car seat is dramatically safer, and it's the only way to guarantee your baby has a spot. For international flights, a lap infant usually costs about 10% of the adult fare plus taxes. Before you book, decide which of those two options you want, because it changes everything about how you buy the ticket and what you pack.
Lap infant vs. buying a seat: what you actually need to decide
Every US airline lets a child under 24 months travel as a "lap infant"—held by an adult for the whole flight. On domestic routes, that's free. It saves money, but understand the trade-offs:
- Safety. The FAA strongly recommends every child, regardless of age, occupy their own seat in an approved child restraint. In turbulence, your arms are not enough to hold a baby. The FAA is blunt about this: your arms are the least effective way to protect your child.
- Space. With a lap infant you get zero extra room. A three-hour flight holding a squirming 20-pound baby on a full plane is its own kind of punishment.
- Guaranteed seat. If you buy a seat, your car seat goes in it and the baby is secured. No fighting for space, no gate agent asking you to gate-check the car seat.
The middle path some parents use: book the lap infant but ask at the gate if there's an open seat next to you. If the flight isn't full, agents will often let you move your car seat into an empty seat for free. It's a gamble on a packed travel day, but on off-peak flights it works often.
Proof of age
Airlines can ask for proof your child is under 2, especially if the kid looks big for their age. Bring a birth certificate, passport, or immunization record. If your baby turns 2 during a round trip, you may need a paid seat for the return leg—check when booking.
How to book each option correctly
This trips people up constantly, so here's the mechanics:
Domestic lap infant: Most airlines don't let you add a lap infant during online booking. Book your own ticket first, then call the airline (or add the infant at check-in) so the baby is on the reservation. That matters because if the plane makes an unscheduled stop or you need to prove who's traveling, you want the infant documented. It also ensures the airline hands out the extra oxygen mask for your row.
International lap infant: Call the airline or book through an agent. You'll pay roughly 10% of the adult fare plus applicable taxes and fees—on a $900 fare to Europe that's around $90 plus taxes. The airline issues a separate infant ticket, and you should get a boarding pass for the baby even though they're on your lap.
Buying a seat for the baby: Book it like any regular passenger. Many airlines offer a discounted "child" fare for infants with their own seat—ask, because it isn't always automatic. You must bring an FAA-approved car seat (look for the label reading "This restraint is certified for use in motor vehicles and aircraft") and the seat must be a window seat so it doesn't block anyone's exit path.
Car seats, strollers, and what flies free
Here's the good news that most parents don't know: baby gear travels free on every major US airline, and it does not count against your checked bag allowance.
| Item | Policy on most US airlines |
|---|---|
| Car seat | Free to check or bring onboard (if you bought a seat). Gate-check available. |
| Stroller | Free. Strollers over ~20 lbs may need to be checked; smaller ones gate-check at the jet bridge. |
| Diaper bag | Free—does not count as your carry-on or personal item on most carriers. |
| Breast pump | Free medical device; doesn't count as a carry-on. |
Gate-checking a stroller and car seat is the standard move: you push the stroller right to the aircraft door, fold it, and hand it to the agent. It's waiting for you at the door when you land (on some smaller regional jets it comes out at baggage claim instead). If gate-checked gear gets damaged or lost, the DOT's baggage liability rules apply—for domestic flights, airlines are liable up to $3,800 per passenger. Photograph your car seat and stroller before you hand them over so you can prove condition if you need to file a claim. Southwest's approach mirrors the majors here; see our breakdown of the Southwest baggage policy for 2026 for the specifics if you're flying them.
Security, boarding, and the airport gauntlet
TSA rules loosen for families, but you still have to know them:
- Liquids for babies are exempt from the 3.4 oz rule. Breast milk, formula, water for mixing formula, and baby food are allowed in "reasonable quantities" over 3.4 oz. Tell the officer you have them before screening. They may test the containers but you don't have to open or taste anything.
- Kids under 12 keep their shoes on and don't need to remove light jackets.
- Car seats and strollers go through the X-ray or get a manual inspection if they don't fit.
- Carry your baby through the metal detector. You can't send a child through on the belt, and you'll usually be asked to walk through the detector holding them.
If you fly with kids more than a couple times a year, TSA PreCheck is worth it—children 12 and under can go through the PreCheck lane with an enrolled parent for free. We compared the options in TSA PreCheck vs. CLEAR vs. Global Entry.
Family boarding: Under a DOT rule that took effect, airlines that offer early family boarding must let families with children under 2 board early at no charge—and several airlines now guarantee families with young kids can sit together without paying seat-selection fees. Ask at the gate; most agents will accommodate families even on basic economy fares.
Delays, cancellations, and your rights with a baby in tow
The US has no EU-style automatic cash payout for delays—no matter how many hours you're stuck with a screaming infant, there's no federal law forcing the airline to pay you for the delay itself. What you do get:
- A cash refund if your flight is cancelled or "significantly changed" and you choose not to travel. Under the 2024 DOT automatic refund rule, the airline must refund you automatically—including any seat fee you paid for the baby—without you begging for it. Refunds go back to your original payment method within 7 business days for credit cards.
- Amenities per the contract of carriage. For long controllable delays, most major carriers provide meal vouchers and hotel rooms. Policies vary; American, United, and Delta all publish their commitments on the DOT dashboard.
- Denied-boarding compensation. If you're bumped from an oversold flight, federal law requires payment—up to 200% of your one-way fare (capped at $1,075) for a 1–2 hour domestic delay, and 400% (capped at $2,150) beyond that. A lap infant with no ticket isn't owed bumping pay, but you are. Read the full breakdown in our guide to denied boarding compensation.
If an airline stonewalls you on a refund or damaged car seat, escalate. Our walkthrough on how to file a DOT complaint gets results faster than arguing at the counter. And if a delay makes you miss a connection, our guide on what to do after a missed flight covers your rebooking options.
Practical tips that make the flight survivable
- Feed on takeoff and landing. Nursing or a bottle helps babies' ears equalize with cabin pressure changes. A pacifier works too.
- Book flights around nap time when you can. A baby who sleeps through a two-hour flight is the goal.
- Pack more diapers than you think. Delays happen. Plan for the trip length plus several hours.
- Bring a change of clothes for both of you. Blowouts at 35,000 feet are not theoretical.
- Ask for a bassinet on long international flights. Airlines mount them on bulkhead walls for infants under a certain weight (usually around 20–25 lbs). Reserve early—there are only a few per cabin.
Frequently Asked Questions
Does a lap infant need a boarding pass?
On domestic flights, not always—but you should still add the infant to your reservation so the airline knows they're aboard. On international flights, the infant gets a separate ticket and you should receive a boarding pass for them. Check them in with an agent if online check-in won't process the infant.
Can I bring my own car seat on the plane?
Yes, if you bought a seat for your child. The car seat must be FAA-approved (check the label for aircraft certification) and typically must go in a window seat. Most car seats fit in economy, but double-check the width against the airline's seat dimensions if you have a bulky model.
What happens if my baby turns 2 during the trip?
Once your child turns 2, they legally need their own paid seat. If they have a birthday between your outbound and return flights, you'll likely fly them as a lap infant one way and need a ticketed seat for the return. Sort this out when booking to avoid a scramble at the airport.
Is it cheaper to fly with a baby internationally as a lap infant?
Usually much cheaper—roughly 10% of the adult fare plus taxes, versus a full or discounted child fare for their own seat. But you'll hold the baby the entire flight, which on a long-haul route is exhausting. If you can afford the seat and bring a car seat, it's safer and far more comfortable for everyone.