Frontier caps a standard checked bag at 40 pounds, not the 50 pounds nearly every other US airline allows. That ten pound gap is the most expensive detail in Frontier baggage rules.
Hit 41 pounds and the fee is $75. The scale does not care that the same bag would have flown free on Delta or American.
What the base fare actually includes
One personal item, 18 by 14 by 8 inches. That is the entire baggage allowance on a standalone Frontier fare.
The carry-on is not included. You buy it separately, or you buy an Economy, Premium or Business bundle that contains it.
The carry-on itself is 24 by 16 by 10 inches at 35 pounds. That is larger than the 22 by 14 by 9 most US carriers use, so a bag sized for Frontier may not fit elsewhere.
The 40 pound checked limit in practice
A standard checked bag is 40 pounds and 62 linear inches. Most travelers pack to a 50 pound habit without thinking about it.
Between 41 and 50 pounds the fee is $75 per bag. From 51 to 99.99 pounds it runs $100 to $129, and the price depends on when you booked.
Nothing at 100 pounds or more is accepted at any price.
Oversize works the same way. Bags from 63 to 110 linear inches cost $75, and anything over 110 inches is refused outright.
Why the fee you are quoted keeps moving
Frontier prices bags dynamically by route and date. There is no single published fee schedule to memorize.
The airline runs a Bag Price Checker, and the price it shows at booking is the cheapest you will see. It rises at check-in, then rises again at the gate.
Buy every bag you know you need while you are still booking.
How Frontier baggage rules compare
The unbundled model itself is not unusual. Allegiant and Avelo sell fares the same way, and Spirit did until it shut down in May 2026.
The 40 pound checked limit is where Frontier stands apart. Allegiant and the major carriers all give you 50.
The oversized carry-on cuts the other way, in your favor. That 24 by 16 by 10 allowance is among the most generous in the US market.
Packing to a Frontier fare
If the personal item can hold the trip, you fly on the price you saw. That is where the fare math actually works.
If you need checked capacity, weigh the bag at home. A luggage scale costs less than a single overweight fee.
Two 40 pound bags often beat one 55 pound bag once the overweight charge lands. Run both numbers in the baggage cost tool before you pay.
What gets enforced at the gate
Frontier is one of the carriers that actively checks personal items against a sizer. Agents are paid a bonus for catching oversized bags, which the airline has confirmed publicly.
Treat the 18 by 14 by 8 figure as a hard number rather than a guideline. A backpack that bulges past the frame counts as oversized.
Paying at the gate is the worst outcome available. That is where Frontier baggage rules cost the most, and it is entirely avoidable.
The bottom line
Frontier baggage rules give you a big carry-on and a small checked allowance. Both are unusual, and the checked side is the one that costs money.
Price the fare with bags added before comparing it to anyone else. Confirm the current figures in the size checker, and see how we verify everything on this page.
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