Route reliability record
SEA→ONT
Seattle to Ontario
- Flights
- 2,487
- Period
- September 2025 to August 2026
- Distance
- 956 mi
- Carriers
- 4
This route lands a B, 5 points better than the national rate of 77.3%. About one flight in six arrives 15 minutes late or worse, and those flights are late by about 50 minutes on average. That rests on 2,487 SEA to ONT flights, of which SkyWest Airlines flew 1,053 at 88.3% on time.
Best time to fly SEA to ONT: a 5am–8am departure, ideally on a Saturday. Flights in that window arrived on time 89.5% of the time and Saturday flights 88.2%, against 82.6% for the route overall.
Set against the rest of the country, this route's record is 5 points better than the US average of 77.3%. That gap is worth roughly 53 fewer late arrivals for every thousand flights.
Key figures
On time
82.6%
Arrivals under 15 minutes late, of 2,461 completed flights
Avg delay
50 min
Across delayed arrivals only, not all flights
Cancelled
1.05%
National rate is 1.89%
Best carrier
SkyWest
88.3% on time across 1,053 flights
These figures cover 2,487 flights between September 2025 and August 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.
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Carrier by carrier
Which airline is most reliable on SEA to ONT
The choice of carrier is not cosmetic here. SkyWest Airlines arrives on time 88.3% of the time; Alaska Airlines manages 77.5%. Sample sizes sit next to every figure, because a two-point gap across 1,257 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Delta Air Linesthin sample | 8 | 100.0% | — | 0.00% | A+ |
| SkyWest Airlines | 1,053 | 88.3% | 52 min | 0.38% | A+ |
| Frontier Airlinesthin sample | 169 | 84.3% | 78 min | 1.78% | B |
| Alaska Airlines | 1,257 | 77.5% | 46 min | 1.51% | B |
SkyWest leads Alaska by 11 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
Flights on SEA to ONT
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
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Best ways to make this trip
The most reliable ways to fly Seattle to Ontario
Every airline on this route and on the routes between nearby airports, ranked by how often a scheduled flight actually operated and arrived on time. 4 of the top 5 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. SEA → LAXSeattle to Los Angeles | United Airlines | 88.8% | 88.8% | 0.00% | 11am–2pm, Fri | — |
| 2. SEA → ONTSeattle to Ontario | SkyWest Airlines | 88.0% | 88.3% | 0.38% | 8am–11am, Sat | OO 4031 14:30 |
| 3. SEA → SNASeattle to Santa Ana | Alaska Airlines | 85.5% | 86.3% | 0.93% | 5am–8am, Tue | AS 699 07:15 |
| 4. SEA → LAXSeattle to Los Angeles | SkyWest Airlines | 84.4% | 85.0% | 0.68% | 11am–2pm, Tue | — |
| 5. SEA → SNASeattle to Santa Ana | Delta Air Lines | 81.6% | 82.4% | 1.01% | 5am–8am, Sat | — |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
Departure window
The best time of day to leave
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 22 points, against 11 points between the best and worst carrier.
- 5am–8am87 flights89.5%
- 8am–11am648 flights89.1%
- 11am–2pm451 flights83.0%
- 2pm–5pm537 flights79.3%
- 5pm–8pm103 flights68.0%
- 8pm–5am661 flights80.2%
Scale runs 60% to 95%.
Book the early departure. Flights leaving between 5am–8am arrive on time 89.5% of the time, against 68.0% for the evening window. That is 22 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8pm–5am window is the busiest, with 661 flights scheduled in it.
Explore
Filter SEA to ONT by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On SEA to ONT, the best departure window is 5am–8am at 89.5% on time and the worst is 5pm–8pm at 68.0%, a wide gap of 21.5 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am89.5%
- 8–11am89.1%
- 11am–2pm83.0%
- 2–5pm79.3%
- 5–8pm68.0%
- 8pm–5am80.2%
best all US flightsScale 60% to 95%.
Across the year
When delays peak on this route
This route's year swings by 23 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
July is the worst month at 67.9% on time, 23 points below September, the best at 91.1%. 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 256 flights.
Across the week, Saturday is the strongest day at 88.2% on time and Thursday the weakest at 79.7%, a spread of 9 points.
Delay causes
Why this route gets delayed
Carrier accounts for 52% of the 21,000 delay minutes carriers reported here, and the remaining four split what is left.
- 52%Carrier
- 26%Late-arriving aircraft
- 15%National Airspace System
- 7%Extreme weather
- 0%Security
The largest share of delay minutes, 52%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 11,000 of the 21,000 delay minutes reported here. The split is drawn from 21,290 reported delay minutes.
Cancellations sit at 1.05% against a national 1.89%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here actually costs
Badly late arrivals are rare here: only 4.2% land an hour or more behind schedule, against 8.3% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
The 956 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.
The return leg is a different operation and performs like one: it runs 85.9% on time across 2,488 flights, 3 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 3 points of difference.
The sample behind these figures is 2,487 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
Work out the risk of missing a connection in ONT after this flight
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. September runs 91.1% on time and July 67.9%, a swing of 23 points. If the dates move at all, move them out of July before you think about anything else. 2,461 completed flights over 12 months sit behind that.
Common questions
SEA to ONT questions
How often is SEA to ONT delayed?
About one flight in six arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 17.4% of the 2,487 flights in this analysis, against 22.7% nationally. Delayed flights are late by about 50 minutes on average.
Which airline is most reliable on SEA to ONT?
SkyWest Airlines leads at 88.3% on time across 1,053 flights. Alaska Airlines is at the other end on 77.5%, a gap of 11 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on SEA to ONT?
The 5am–8am departure window is the strongest at 89.5% on time. The 5pm–8pm window is the weakest at 68.0%, 22 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are July delays on SEA to ONT?
July is the weakest month at 67.9% on time, compared with 91.1% in September. Across the year that is 23 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- ONT to SEA — the return legseparate record
- Seattle-Tacoma International (SEA) delay statistics
- Ontario International (ONT) delay statistics
- SkyWest Airlines on SEA to ONT88.3%
- Frontier Airlines on SEA to ONT84.3%
- Alaska Airlines on SEA to ONT77.5%
- SEA to LAX, a related route82.0%
- PHX to ONT, a related route76.8%
- SEA to PHX, a related route78.2%
- Delta Air Lines on-time record100.0%
- SkyWest Airlines on-time record88.3%
- Frontier Airlines on-time record84.3%
- Same route, different airline: where the carrier you pick matters most
- The best time of day to fly, according to 7.05 million flight records
Direction matters. SEA to ONT and ONT to SEA are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.