The Fees Got Worse in 2026
Frontier now charges $59 to $79 for a carry-on if you pay at the gate. Spirit's gate fee runs $65 to $89. Allegiant hits $75 at the airport. These aren't edge cases — they're the default outcome when you show up with a bag that's one inch too big. The airlines make more on fees than on tickets, so they measure hard and they don't negotiate. The fix is boring: know the exact dimensions, measure your bag at home, and buy the right ticket class.
Know the Real Dimensions
A personal item on Spirit is 18 x 14 x 8 inches. Frontier is 18 x 14 x 8. Allegiant is 16 x 15 x 7. That's smaller than most people think — a standard school backpack often fails. The carry-on limit is 22 x 14 x 9 on Spirit and Frontier. Measure your bag with a tape measure, wheels and handles included. If it's 23 inches, it's a carry-on fee. If it's 9.5 inches deep, same. Write the numbers on a sticky note and tape it inside your closet so you stop guessing.
Book the Bundle, Not the Base Fare
Spirit's base fare looks cheap until you add a carry-on. In 2026, a Spirit 'Bundle' fare that includes a carry-on and seat selection often costs $30 to $45 more than base — cheaper than the $65 gate fee. Frontier's 'Discount Den' membership ($99 per year) drops carry-on prices to $30 to $40 and lets you book a second bag free on some fares. Run the math before you book: base fare plus bag fee versus bundle price. The bundle wins about 70 percent of the time on routes over two hours.
The Personal-Item-Only Strategy
For trips of three days or less, skip the carry-on entirely. A 16 x 15 x 7 inch underseat bag holds three t-shirts, one pair of pants, underwear, a toothbrush, and a phone charger. Wear your bulkiest shoes and jacket on the plane. Frontier and Spirit both allow one personal item free. I've done four days in Austin on a personal item by packing two merino shirts that don't wrinkle and washing socks in the sink. The savings: $59 to $79 each way.
Measure at the Gate, Not the Counter
Gate agents use a metal sizer. If your bag doesn't slide in, you pay. The sizer is slightly smaller than the published dimensions because it accounts for wheels. So if your bag is exactly 22 x 14 x 9, it may still fail. Aim for 21 x 13 x 8 to leave margin. Soft-sided bags compress; hard-shell bags don't. A $40 soft duffel from Amazon beats a $300 hard-shell roller that fails the sizer by half an inch.
When to Just Pay the Fee
If you're flying with a family of four and need real luggage, the fee math changes. Four carry-ons at $65 each is $260 round trip. At that point, check one large bag for $70 and carry personal items only. Or book Southwest, which still includes two free checked bags on most fares in 2026. The rule: if your total bag fees exceed $120 round trip, compare against a full-service airline's ticket price. Sometimes the 'expensive' airline is cheaper.
The Bottom Line
Budget airlines are fine if you play by their rules. Measure your bag. Book the bundle when it's cheaper than the gate fee. Pack a personal item for short trips. And never, ever show up at the gate with an unmeasured bag — that's a $75 mistake you can avoid with a $10 tape measure.