Route reliability
Denver (DEN) to Seattle (SEA): which airline is most on time?
On-time arrivals, cancellations and long delays for every airline that reported nonstop flights from Denver, CO (DEN) to Seattle, WA (SEA), September 2025 to August 2026.
Denver, COSeattle, WA
Route at a glance · September 2025 to August 2026
DEN to SEA
Denver, CO to Seattle, WA
- On time
- 74.0%vs 75.6% U.S. average Worse than average
- Cancelled
- 0.6%vs 1.9% U.S. average Better than average
- 60+ min late
- 7.2%vs 8.1% U.S. average About average
- Scheduled flights
- 6,328in 12 months6 airlines
- Most reliable airline
- Frontier Airlines81.8% on time · 439 flights
On time less often than the U.S. average, with fewer cancellations.
Airlines on this route
Ranked by on-time arrival
| Airline | On time | Cancelled | 60+ min late | Avg delay when late | Diverted | Flights |
|---|---|---|---|---|---|---|
| 1. Frontier Airlines Most reliable | 81.8% | 1.1% | 5.0% | 54 min | 0.0% | 439 |
| 2. United Airlines | 80.5% | 0.5% | 5.8% | 57 min | 0.0% | 1,908 |
| 3. Delta Air Lines | 77.8% | 0.9% | 7.0% | 85 min | 0.0% | 868 |
| 4. SkyWest Airlines Operating carrier; sold as United Express, Delta Connection, American Eagle, Alaska Small sample (under 300 flights) | 75.5% | 0.5% | 9.1% | 70 min | 0.0% | 220 |
| 5. Alaska Airlines | 74.3% | 0.7% | 6.7% | 58 min | 0.0% | 1,551 |
| 6. Southwest Airlines | 59.2% | 0.3% | 10.4% | 49 min | 0.1% | 1,342 |
On time = arrived within 15 minutes of schedule. Avg delay when late = average arrival delay of flights 15+ minutes late. "Most reliable" needs at least 300 flights in 12 months. Tap a heading to sort.
What this means
Frontier Airlines has the strongest record on this route.
- Frontier Airlines had the best on-time record from Denver (DEN) to Seattle (SEA): 81.8% of its 439 scheduled flights arrived within 15 minutes of schedule, compared with 59.2% for Southwest Airlines.
- 0.6% of flights on this route were cancelled (about 1 in 167), 1.3 points lower than the U.S. average of 1.9%.
- 7.2% of flights, about 1 in 14, arrived an hour or more late. When a flight was late (15+ minutes), the average arrival delay was 58 min.
- Overall, 74.0% of flights on this route arrived on time, 1.6 points lower than the U.S. average of 75.6%.
- Over the last 3 years, November was the most reliable month on this route (82.3% on time) and June the least reliable (64.4%).
- Flights scheduled to depart 7 am to 8 am were the most punctual (89.7% on time); flights scheduled to depart 6 pm to 7 pm were the least (56.0%).
- In the other direction, Seattle (SEA) to Denver (DEN), 77.3% of flights were on time and 0.7% were cancelled. Compare airlines SEA to DEN.
Best and worst months to fly DEN to SEA
Share of scheduled flights on time 12-month average 74.0%
Show as table
| Period | On time | Flights |
|---|---|---|
| January | 76.5% | 1,360 |
| February | 77.0% | 1,259 |
| March | 74.7% | 1,421 |
| April | 78.7% | 1,456 |
| May | 72.8% | 1,708 |
| June | 64.4% | 1,961 |
| July | 68.0% | 2,066 |
| August | 65.6% | 1,970 |
| September | 79.6% | 1,793 |
| October | 81.6% | 1,710 |
| November | 82.3% | 1,470 |
| December | 77.4% | 1,469 |
| Airline | Best month | Worst month |
|---|---|---|
| Frontier Airlines | September (82.8%) | March (62.1%) |
| United Airlines | September (87.3%) | August (71.2%) |
| Delta Air Lines | October (86.6%) | June (71.9%) |
| Alaska Airlines | October (84.0%) | August (62.7%) |
| Southwest Airlines | November (78.4%) | June (46.6%) |
Month by month, last 12 months
Share of scheduled flights on time U.S. average 75.6%
Show as table
| Period | On time | Flights |
|---|---|---|
| Sep 2025 | 78.6% | 575 |
| Oct 2025 | 79.2% | 552 |
| Nov 2025 | 82.5% | 464 |
| Dec 2025 | 58.8% | 468 |
| Jan 2026 | 83.0% | 430 |
| Feb 2026 | 83.3% | 401 |
| Mar 2026 | 67.7% | 455 |
| Apr 2026 | 83.8% | 469 |
| May 2026 | 76.6% | 546 |
| Jun 2026 | 68.8% | 634 |
| Jul 2026 | 69.9% | 678 |
| Aug 2026 | 63.6% | 656 |
Best and worst departure times
Share of scheduled flights on time
Show as table
| Period | On time | Flights |
|---|---|---|
| Departing before 6 am | Insufficient sample | 11 |
| Departing 6 am to 7 am | 88.2% | 612 |
| Departing 7 am to 8 am | 89.7% | 516 |
| Departing 8 am to 9 am | 82.4% | 631 |
| Departing 9 am to 10 am | 77.3% | 225 |
| Departing 10 am to 11 am | 72.2% | 108 |
| Departing 11 am to noon | 83.1% | 472 |
| Departing noon to 1 pm | 73.7% | 509 |
| Departing 1 pm to 2 pm | 78.9% | 399 |
| Departing 2 pm to 3 pm | 73.7% | 95 |
| Departing 3 pm to 4 pm | 70.9% | 399 |
| Departing 4 pm to 5 pm | 67.0% | 352 |
| Departing 5 pm to 6 pm | 64.2% | 162 |
| Departing 6 pm to 7 pm | 56.0% | 411 |
| Departing 7 pm to 8 pm | 65.7% | 741 |
| Departing 8 pm to 9 pm | 62.4% | 274 |
| Departing 9 pm to 10 pm | 58.3% | 338 |
| Departing 10 pm to 11 pm | 53.4% | 73 |
Sources & data dates
- Source
- U.S. DOT Bureau of Transportation Statistics, Reporting Carrier On-Time Performance (1987-present)
- Period
- September 2025 to August 2026 (12 months); month-of-year patterns September 2023 to August 2026
- Data through
- August 2026
- Processed
- 2026-11-03
- Scope
- Nonstop scheduled flights from Denver, CO (DEN) to Seattle, WA (SEA), one direction. Airlines that report to the DOT only.
- Method
- Rates use all scheduled flights as the denominator; cancelled and diverted flights count as not on time. Figures based on fewer than 50 scheduled flights are suppressed. Full methodology.