Carrier route record
DLSEA→DEN
Delta Air Lines · Seattle to Denver
- Flights
- 869
- Period
- July 2025 to June 2026
- Share of route
- 14%
- Carriers
- 6
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Delta Air Lines.
Delta 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, 4 points worse than the national rate of 77.6%. The late ones land about an hour behind schedule. That rests on 869 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
73.3%
Arrivals under 15 minutes late, of 857 completed flights
Avg delay
58 min
Across delayed arrivals only, not all flights
Cancelled
0.92%
National rate is 1.81%
Whole route
77.8%
Every carrier on SEA to DEN, 6,317 flights
These figures cover 869 flights between July 2025 and June 2026. The median arrival is 5 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.
Carrier by carrier
Delta against every carrier on SEA to DEN
Delta flew 869 of the 6,317 flights on SEA to DEN, about 14% of it. Its 73.3% on time is 5 points worse than the route as a whole, which runs 77.8%. Ranked by on-time rate it is number five 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 | 419 | 74.9% | 75 min | 1.91% | C |
| Delta Air Lines (this page) | 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.
Departure window
When Delta runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 46 points, against 19 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am188 flights82.3%
- 8am–11am79 flights86.1%
- 11am–2pm43 flights40.5%
- 2pm–5pm194 flights60.6%
- 5pm–8pm285 flights76.7%
- 8pm–5am80 flights74.7%
Scale runs 30% to 90%. Rows with fewer than 30 flights show a dash.
The weak window here is the middle of the day, not the evening: 11am–2pm runs 40.5% on time against 86.1% for 8am–11am. That shape usually means a departure bank rather than an accumulating delay, so the recovery later in the afternoon is real rather than noise. The 5pm–8pm window is the busiest, with 285 flights scheduled in it.
Across the year
Delta on SEA to DEN through the year
July is the worst month at 61.1% on time, 24 points below November, the best at 85.1%. 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. July was the busiest month here, with 93 flights.
Across the week, Wednesday is the strongest day at 78.3% on time and Sunday the weakest at 69.4%. 9 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Delta runs late on this route
One category carries most of the weight here. Carrier accounts for 51% of the 13,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.
- 51%Carrier
- 26%National Airspace System
- 22%Late-arriving aircraft
- 1%Extreme weather
The largest share of delay minutes, 51%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 6,769 of the 13,000 delay minutes reported here. The split is drawn from 13,335 reported delay minutes.
Cancellations sit at 0.92% against a national 1.81%, which is ordinary. Diversions add another 0.46%.
Connections and stage length
What a delay here costs
7.9% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last about an hour, which a normal layover absorbs.
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 is a different operation and performs like one: it runs 79.2% on time across 868 flights, 6 points above this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 6 points of difference.
One caution: this is a thin sample. 869 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 Delta on SEA to DEN
Put together: treat all of this as provisional. 869 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 73.3% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 857 completed flights over 12 months sit behind that.
Related
Where to go next
- SEA to DEN, every carrier
- Delta 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%
- Frontier Airlines on SEA to DEN74.9%
- Southwest Airlines on SEA to DEN69.0%
- Delta Air Lines 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
- The best time of day to fly, according to 7.04 million flight records
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.