85% of flights from Ontario to Seattle arrived on time over the past 12 months. That is better than the typical U.S. route. The 7 a.m. departures ran on time 94% of the time; the 7 p.m. ones 68%. Most reliable airline: Delta Air Lines (91%). 5% of flights arrived more than an hour late or not at all.
How late?
The on-time rate treats a flight 20 minutes late the same as one 5 hours late. Here's the split for ONT → SEA: when a flight was late, it was under 45 minutes late 63% of the time. About 1 in 27 flights landed an hour or more late, and 1 in 108 three hours or more; 1.1% were cancelled outright.
- On time or early85%
- 15–30 min late6.4%
- 30–60 min late3.9%
- 1–2 hours late1.8%
- 2–3 hours late0.9%
- 3+ hours late0.9%
- Diverted0.1%
- Cancelled1.1%
Share of all 2,488 scheduled flights, past 12 months, by arrival time against schedule.
By airline
| Airline | Flights | On time | Cancelled | Typical arrival | 1h+ late | Avg when late | Operated by |
|---|---|---|---|---|---|---|---|
| Alaska Airlines | 1,258 | 81% | 1.8% | −6 min | 4.2% | +54 min | Alaska Airlines 100%, SkyWest 0% |
| Delta Air Lines | 1,061 | 91% | 0.3% | −12 min | 2.6% | +95 min | SkyWest 99%, Delta Air Lines 1% |
| Frontier Airlines | 169 | 76% | 1.8% | −11 min | 5.9% | +80 min | Frontier Airlines |
Airline = the name on the ticket. Regional flights (e.g. "Delta Connection") count under the ticketing airline, and the operator is listed.
Best time of day to fly
On-time rate by scheduled departure hour (local time at ONT). Delays build through the day as late planes knock on, so early flights usually do best.
By airline and hour
| Departs | Alaska Airlines | Delta Air Lines |
|---|---|---|
| 6 a.m. | 92% | 94% |
| 7 a.m. | — | 94% |
| 11 a.m. | — | 92% |
| noon | 80% | — |
| 4 p.m. | 76% | — |
| 5 p.m. | — | 88% |
| 7 p.m. | 68% | — |
Last flight of the day
On ONT → SEA, each airline's last flight of the day was cancelled 0.4% of the time, against 1.4% for its earlier flights, so here the last flight is actually the safer one. It arrived 3+ hours late 1.4% of the time (earlier flights: 0.6%). It matters more than the numbers suggest. Miss an earlier flight and there's another one that evening; miss the last one and you're usually waiting until morning.
| Airline | Last departure | Last: cancelled | Last: 3h+ late | Earlier: cancelled | Next morning |
|---|---|---|---|---|---|
| Alaska Airlines | 7:59 p.m. | 0.5% | 1.6% | 2.2% | first flight 6:02 a.m. |
| Delta Air Lines | 6:01 p.m. | 0.3% | 1.1% | 0.3% | first flight 6:20 a.m. |
Last flight = the airline's last scheduled departure on this route that day, on days it flies the route at least twice; past 12 months. Times are typical scheduled times over the latest three months.
By month
Each calendar month pooled over 2023–2026. Best: April (91%). Worst: July (80%).
By day of week
| Day | Flights | On time | Cancelled |
|---|---|---|---|
| Monday | 391 | 82% | 0.5% |
| Tuesday | 335 | 89% | 0.0% |
| Wednesday | 326 | 86% | 0.6% |
| Thursday | 364 | 82% | 0.8% |
| Friday | 380 | 84% | 2.6% |
| Saturday | 309 | 87% | 1.6% |
| Sunday | 383 | 85% | 1.6% |
Why flights were late
Share of delay minutes on flights 15+ minutes late, as reported to BTS by the airlines.
Cancellations: airline 18 · air traffic/airport 7 · weather 3
Month by month
Flight numbers on this route
Regular flights with at least 120 scheduled trips in the past year. Sorted by departure time.
| Flight | Departs | Flights | On time | Cancelled | Typical arrival | Operated by |
|---|---|---|---|---|---|---|
| AS 607 | 6:00 a.m. | 294 | 93% | 0.7% | −10 min | Alaska Airlines |
| DL 4070 | 11:59 a.m. | 177 | 90% | 0.0% | −12 min | SkyWest |
| AS 654 | 12:04 p.m. | 310 | 84% | 3.5% | −9 min | Alaska Airlines |
| F9 2275 | 4:49 p.m. | 126 | 75% | 2.4% | −11 min | Frontier Airlines |
| DL 4031 | 5:50 p.m. | 322 | 88% | 0.3% | −11 min | SkyWest |
| AS 594 | 9:20 p.m. | 137 | 66% | 0.0% | 0 min | Alaska Airlines |
Worst days in the past year
| Date | Flights | On time | Cancelled |
|---|---|---|---|
| Mar 13, 2026 | 6 | 0% | 3 |
| Jul 16, 2026 | 9 | 11% | 0 |
| Aug 9, 2026 | 9 | 33% | 1 |
| Dec 31, 2025 | 5 | 40% | 0 |
| Aug 10, 2026 | 9 | 44% | 0 |
Nearby airport alternatives
Other ways to make the same trip, using airports within 60 miles of Ontario or Seattle. None has been clearly more reliable than ONT → SEA.
| Route | Flights | On time | Cancelled |
|---|---|---|---|
| ONT → SEA (this route) | 2,488 | 85% | 1.1% |
| SNA → SEA Orange County John Wayne to Seattle-Tacoma | 3,944 | 85% | 1.1% |
| LAX → SEA Los Angeles LAX to Seattle-Tacoma | 7,544 | 84% | 0.8% |
| BUR → SEA Hollywood Burbank to Seattle-Tacoma | 1,653 | 82% | 2.4% |
Questions
How often are flights from ONT to SEA on time?
85% of 2,488 scheduled flights from Ontario, CA to Seattle, WA arrived within 15 minutes of schedule between September 2025 and August 2026. 1.1% were cancelled.
What is the best time of day to fly ONT to SEA?
Flights scheduled to leave at 7 a.m. were the most reliable (94% on time). The 7 p.m. departures were the least (68%).
Which airline is most on time from ONT to SEA?
Delta Air Lines: 91% of its 1,061 flights on the route arrived on time. Alaska Airlines: 81%. Frontier Airlines: 76%.
What month has the most delays from ONT to SEA?
July (80% on time). The best month is April (91%), over 2023–2026.
Is the last flight of the day from ONT to SEA more likely to be cancelled?
No, the opposite. Each airline's last ONT–SEA flight of the day was cancelled 0.4% of the time over the past year, against 1.4% for its earlier flights. If the last flight is cancelled, the next one is usually the following morning.
Related
- SEA → ONT (return)
- Ontario (ONT) delays by hour
- Flights into Seattle-Tacoma (SEA)
- Alaska Airlines on-time record
- Delta Air Lines on-time record
- Frontier Airlines on-time record
- Connecting off this flight? Check the risk
Domestic flights by the airlines that report to the U.S. DOT, plus their regional partners. "On time" means arriving less than 15 minutes after schedule; cancelled and diverted flights count as not on time. Past performance is a guide, not a forecast. Method.