Last March, I booked what looked like a $59 Spirit flight from Chicago to Orlando. By the time I'd added a carry-on, picked a seat that wasn't in the last row next to the lavatory, and paid the booking fee, it was $127. Still cheaper than United — but not by as much as that $59 made me feel.
That's the game with ultra-low-cost carriers (ULCCs), and if you're going to play it, you need to know the rules for each airline before you click "book." Spirit, Frontier, and Sun Country are the three main budget options for domestic US travel in 2026, and they are not interchangeable. They have different fee structures, different network strengths, and wildly different reputations for the thing that matters most when you're in seat 28F: whether the plane actually takes off on time.
Let's get into it.
The base fare illusion: what you're actually paying
All three airlines advertise fares that look almost insultingly cheap. Spirit and Frontier regularly post $29–$49 base fares on competitive routes. Sun Country tends to start a little higher — think $49–$79 — but the gap closes fast once you start adding things that other airlines include by default.
Here's a realistic price breakdown for a round trip from Minneapolis (MSP) to Phoenix (PHX) in March 2026, one of the most price-competitive leisure routes in the country:
| Spirit | Frontier | Sun Country | |
|---|---|---|---|
| Base fare (RT) | $78 | $72 | $104 |
| Carry-on bag (RT) | $90 | $100 | $60 |
| Seat selection | $20–$50 | $15–$45 | $15–$30 |
| Booking fee (online) | $0 | $0 | $0 |
| Realistic total | $188–$218 | $187–$217 | $179–$194 |
The takeaway: never compare base fares between these three. Compare the full cart total for your specific itinerary, with your specific bags.
Spirit Airlines: the original fee machine
Spirit invented a lot of the unbundling tricks that Frontier later copied and refined. Every single thing costs extra — carry-ons, seat selection, printing your boarding pass at the airport ($25, by the way, so don't forget to download it), even water on board.
What Spirit does well is network density. They fly to over 90 destinations across the US, Caribbean, and Latin America, with a particular stranglehold on South Florida. If you're flying out of Fort Lauderdale (FLL), Spirit often has no real competition on price. I've seen FLL-BOS fares at $49 one-way when JetBlue was charging $189 for the same date.
Spirit's Big Front Seat is worth knowing about. It's not business class — there's no lie-flat anything — but it's a wider seat with more legroom, sold à la carte for usually $25–$60 extra. On a 3-hour flight, that's sometimes worth it if you're tall or just done with middle seats.
The problem is reliability. Spirit's on-time performance has historically been among the worst in the US industry. In 2025, Spirit ranked last or near-last in DOT on-time arrival statistics for the fifth consecutive year. If your Spirit flight connects, budget extra time. If it doesn't connect, you're probably fine — their point-to-point network means most routes are nonstop.
Pro Tip: Spirit's "Saver$ Club" membership ($69.95/year) unlocks lower bag fees and member-only fares. If you fly Spirit more than twice a year with a carry-on, it pays for itself on the bag fees alone.
Frontier Airlines: the fee structure got complicated
Frontier went through a significant rebrand in the last few years, trying to position itself as slightly more premium than Spirit while keeping fares in the same ZIP code. The results are... mixed.
The big Frontier play right now is their "All-You-Can-Fly" pass, which launched in 2024 and has been iterated on since. For around $599/year (prices fluctuate), you get unlimited standby flights on Frontier's network. It sounds incredible. In practice, it works well if you live near a Frontier hub (Denver is the big one), travel with zero checked bags, and have flexible schedules. It's a disaster if you have any of those variables wrong.
For regular ticket buyers, Frontier's fee table is genuinely confusing. Bag fees vary by route, by how far in advance you book, and by whether you're an "Elite" member. A carry-on from Denver to Las Vegas might cost $39 if you book it when you buy the ticket, $59 if you add it later online, and $99 at the gate. That gate fee is not a typo.
| Bag type | At booking | Online later | At gate |
|---|---|---|---|
| Personal item (fits under seat) | Free | Free | Free |
| Carry-on | $39–$59 | $49–$79 | $89–$99 |
| First checked bag | $39–$49 | $49–$59 | $69–$79 |
On-time performance: slightly better than Spirit, not dramatically so. Frontier finished 2025 in the bottom third of US carriers for on-time arrivals.
Sun Country Airlines: the one people actually like
Sun Country is the odd one out here. Based in Minneapolis, it's smaller (around 50 destinations versus Spirit's 90+), more seasonal, and — and this is the part that surprises people — it has a real reputation for not being terrible.
J.D. Power's 2025 North America Airline Satisfaction Study ranked Sun Country significantly higher than Spirit or Frontier for economy class experience. That's not nothing. When you're stuck on a 4-hour flight, "not being terrible" has real value.
What makes Sun Country different structurally is that it operates more like a hybrid between a ULCC and a charter airline. They do package deals with hotels, they have a real loyalty program that earns actual miles, and their carry-on bag fees are consistently lower than Frontier or Spirit. A carry-on runs $35–$50 on most Sun Country routes versus $39–$99 on Frontier.
They also have assigned seating that doesn't feel punitive. Spirit and Frontier both have seat selection systems designed to make you feel like you're being punished if you don't pay. Sun Country's cheapest seats are still in reasonable locations — you're not automatically assigned to the middle seat in the last row.
The catch: if you're not near Minneapolis or one of their seasonal focus cities (think Cabo San Lucas, Montego Bay, or Florida beach towns in winter), Sun Country probably isn't flying your route. Their network is intentional and thin. That's not a criticism — it's just the reality of a smaller airline with a regional identity.
Baggage fees: the real comparison
I've said it once but it bears a dedicated section because this is where people get burned. Here's the honest summary:
Spirit: Expensive bags, but predictable pricing if you add them at booking. Personal item (must fit under seat) is free. A carry-on runs $45–$65 at booking, $79–$89 at the gate. First checked bag is $45–$65 at booking. Frontier: The most variable bag pricing of the three. Cheapest if you add bags at booking on short routes, most expensive at the gate of any US carrier. The "WORKS" bundle ($79–$99 one-way) includes a carry-on, seat selection, and a refundable ticket — worth doing the math on if you'd otherwise pay for those separately. Sun Country: Lowest carry-on fees of the three in most scenarios. First checked bag runs $35–$50. If you're a one-carry-on traveler, Sun Country is almost always the cheapest all-in.The FlightKitten catch alerts for these airlines always show base fares, so when you get a pounce alert for a $39 Frontier fare, remember to add roughly $35–$60 for a carry-on before you decide it's a deal worth jumping on.
On-time performance and reliability
This matters more than people admit when they're staring at a $49 base fare.
The DOT publishes monthly on-time performance data, and the 2025 full-year numbers tell a clear story:
| Airline | 2025 on-time arrival rate | Industry average |
|---|---|---|
| Sun Country | 78.4% | 76.2% |
| Frontier | 71.8% | 76.2% |
| Spirit | 68.3% | 76.2% |
Spirit's issues aren't random — they're structural. A lean fleet with minimal spare aircraft means a delay in Denver cascades into cancellations in Dallas and Orlando by evening. They've been working on it for years. The numbers still show they haven't fixed it.
Pro Tip: For any of these three airlines, book the first flight of the day when possible. Aircraft overnighting at your departure airport means there's no upstream delay to inherit. I've had perfect Spirit flights at 6am and miserable ones at 7pm on the same route.
Which routes is each airline actually best for?
Stop thinking about which airline is "best" in the abstract. Think about which airline dominates the specific route you're flying.
Spirit wins on: FLL-based routes, Caribbean routes (San Juan, Montego Bay, Nassau), and any route where they're the only ULCC option. Also strong on DTW, LAS, and MCO. Frontier wins on: Denver (DEN) is their fortress — they have more flights out of DEN than any other ULCC, and prices reflect that competition. Also strong on routes to secondary leisure cities that Spirit ignores. Sun Country wins on: MSP routes, obviously, but also winter sun routes from the Midwest (MSP, MKE, MSN) to Florida and Mexico. If you're flying Minneapolis to Cancun in February, Sun Country's all-in price will likely beat both competitors while also being more pleasant.FlightKitten's hunt feature lets you set up watchlists for specific routes across multiple airlines, so you're not manually checking three different sites every week. Set the hunt, get the pounce alert, then do the all-in math before you book.
The verdict: who should fly which airline
There's no universal winner here, which I know is annoying, but it's the honest answer.
Fly Spirit if: You're departing from a Spirit hub (especially FLL or DTW), you travel with only a personal item that truly fits under the seat, and you're comfortable with the reliability risk. The fares are genuinely cheap on the right routes. Fly Frontier if: You're based near Denver, you can commit to adding bags at booking (never at the gate, ever), or you're seriously considering the All-You-Can-Fly pass and have the schedule flexibility to make it work. Fly Sun Country if: You're anywhere near Minneapolis, you're doing a winter leisure trip from the Midwest, or you just want the budget price without the budget experience. Their carry-on fees are lower, their planes run closer to on time, and their passengers seem measurably less miserable.The dirty secret of budget airline travel is that the "cheapest" airline is almost never the same airline twice in a row. It depends on the route, the date, your bag situation, and whether you value your time enough to pay $20 more to not sit in seat 34E.
Set up your hunts on FlightKitten for the routes you care about, let the pounce alerts do the monitoring work, and when a catch comes in — do the full math before you commit. That $59 fare is sometimes a genuine steal. And sometimes it's $127 with a middle seat.
Either way, now you know what you're getting into.
