Carrier route record
F9SEA→DEN
Frontier Airlines · Seattle to Denver
- Flights
- 419
- Period
- July 2025 to June 2026
- Share of route
- 7%
- Carriers
- 6
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Frontier Airlines.
Frontier on SEA to DEN sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.6%. The late ones land a little over an hour behind schedule. That rests on 419 flights. The strongest carrier on the route with a full sample, United Airlines, flew 1,905 at 87.5% on time.
United Airlines is the most reliable of the four carriers covered here at 87.5% on time across 1,905 flights.
Key figures
On time
74.9%
Arrivals under 15 minutes late, of 411 completed flights
Avg delay
75 min
Across delayed arrivals only, not all flights
Cancelled
1.91%
National rate is 1.81%
Whole route
77.8%
Every carrier on SEA to DEN, 6,317 flights
These figures cover 419 flights between July 2025 and June 2026. Beyond the headline rate, 9.2% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.
Carrier by carrier
Frontier against every carrier on SEA to DEN
Frontier flew 419 of the 6,317 flights on SEA to DEN, about 7% of it. Its 74.9% on time is 3 points worse than the route as a whole, which runs 77.8%. Ranked by on-time rate it is number four of six carriers on the route, where the range runs from United at 87.5% to Southwest at 69.0%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The choice of carrier is not cosmetic here. United Airlines arrives on time 87.5% of the time; Southwest Airlines manages 69.0%. Sample sizes sit next to every figure, because a two-point gap across 1,345 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 1,905 | 87.5% | 73 min | 0.84% | A+ |
| SkyWest Airlinesthin sample | 221 | 85.0% | 60 min | 0.45% | A+ |
| Alaska Airlines | 1,558 | 75.9% | 50 min | 0.83% | B+ |
| Frontier Airlines (this page) | 419 | 74.9% | 75 min | 1.91% | C |
| Delta Air Lines | 869 | 73.3% | 58 min | 0.92% | C+ |
| Southwest Airlines | 1,345 | 69.0% | 52 min | 0.59% | C+ |
The spread between United and Southwest is 19 points, wide enough that it should decide the booking. On a hundred trips that is 19 more arrivals inside the on-time window.
Flight by flight
Frontier flight numbers on SEA to DEN
Departure window
When Frontier runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 14 points, against 19 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am98 flights69.8%
- 8am–11am—
- 11am–2pm105 flights81.9%
- 2pm–5pm90 flights70.1%
- 5pm–8pm71 flights71.0%
- 8pm–5am55 flights83.3%
Scale runs 60% to 90%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is the strongest at 83.3% on time. The full set of windows spans 14 points.
Across the year
Frontier on SEA to DEN through the year
July is the worst month at 56.2% on time, 31 points below May, the best at 87.5%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. June was the busiest month here, with 57 flights.
Across the week, Sunday is the strongest day at 80.0% on time and Tuesday the weakest at 68.3%. 12 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Frontier runs late on this route
Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 7,705 reported delay minutes.
- 36%National Airspace System
- 33%Late-arriving aircraft
- 28%Carrier
- 3%Extreme weather
36% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 2,788 minutes out of 7,705, against a national NAS share of 21%. The split is drawn from 7,705 reported delay minutes.
Cancellations sit at 1.91% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 9.2% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.
The 1,024 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.
The return leg runs 74.9% on time across 419 flights, within half a point of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
One caution: this is a thin sample. 419 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
What to do with this
Booking Frontier on SEA to DEN
Put together: treat all of this as provisional. 419 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 74.9% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 411 completed flights over 12 months sit behind that.
Related
Where to go next
- SEA to DEN, every carrier
- Frontier on DEN to SEA, the return leg
- United Airlines on SEA to DEN87.5%
- SkyWest Airlines on SEA to DEN85.0%
- Alaska Airlines on SEA to DEN75.9%
- Delta Air Lines on SEA to DEN73.3%
- Southwest Airlines on SEA to DEN69.0%
- Frontier Airlines network-wide record
- Seattle-Tacoma International (SEA) delay statistics
- Denver International (DEN) delay statistics
- Same route, different airline: where the carrier you pick matters most
- Why the first flight of the morning is statistically safest
Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.