Carrier route record

F9SEA→ONT

Frontier Airlines · Seattle to Ontario

Flights: 169
Period: July 2025 to June 2026
Share of route: 7%
Carriers: 4

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Frontier Airlines.

Frontier on SEA to ONT lands a B, about a point better than the national rate of 77.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by a little over an hour on average. That is a workable record, not a spotless one. That rests on 169 flights. The strongest carrier on the route with a full sample, SkyWest Airlines, flew 1,084 at 89.7% on time.

The US average over the same twelve months is 77.6%, so there is little to separate Frontier on SEA to ONT from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.

On time

78.4%

Arrivals under 15 minutes late, of 167 completed flights

Avg delay

77 min

Across delayed arrivals only, not all flights

Cancelled

1.18%

National rate is 1.81%

Whole route

82.9%

Every carrier on SEA to ONT, 2,550 flights

These figures cover 169 flights between July 2025 and June 2026. Beyond the headline rate, 9.0% 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 ONT

Frontier flew 169 of the 2,550 flights on SEA to ONT, about 7% of it. Its 78.4% on time is 5 points worse than the route as a whole, which runs 82.9%. Ranked by on-time rate it is number three of four carriers on the route, where the range runs from Delta at 93.1% to Alaska at 77.4%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The choice of carrier is not cosmetic here. SkyWest Airlines arrives on time 89.7% of the time; Alaska Airlines manages 77.4%. Sample sizes sit next to every figure, because a two-point gap across 1,268 flights means less than a ten-point one.

On-time performance by carrier on SEA to ONT
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Linesthin sample	29	93.1%	32 min	0.00%	A+
SkyWest Airlines	1,084	89.7%	52 min	0.37%	A+
Frontier Airlines (this page)thin sample	169	78.4%	77 min	1.18%	B
Alaska Airlines	1,268	77.4%	47 min	2.05%	B

The spread between SkyWest and Alaska is 12 points, wide enough that it should decide the booking. On a hundred trips that is 12 more arrivals inside the on-time window.

Departure window

When Frontier runs best on this route

Departure time is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 169 flights.

There are not enough flights in each departure window to split Frontier's SEA to ONT record by time of day without the percentages moving on noise. The headline rate of 78.4% is the reliable figure here.

Across the year

Frontier on SEA to ONT through the year

Jul–Sep 202580 flights74.7%
Oct–Dec 202546 flights71.7%
Jan–Mar 20266 flights—
Apr–Jun 202637 flights91.7%

Scale runs 65% to 95%. Rows with fewer than 30 flights show a dash.

Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 78.4% on time across 169 flights.

Frontier on SEA to ONT did not run the same all year. Its best quarter was Apr–Jun 2026 at 91.7% on time and its weakest Oct–Dec 2025 at 71.7%, a swing of 20 points on roughly 56 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.

Across the week, Sunday is the strongest day at 88.2% on time and Monday the weakest at 66.7%. 22 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Frontier runs late on this route

One category carries most of the weight here. Carrier accounts for 50% of the 2,761 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.

Carrier
50%
Late-arriving aircraft
41%
National Airspace System
9%
Extreme weather
0%

41% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 2,761 reported delay minutes here, that single category outweighs weather by 41 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 2,761 reported delay minutes.

The largest share of delay minutes, 50%, 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 1,374 of the 2,761 delay minutes reported here.

Cancellations sit at 1.18% 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. 9.0% 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 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. 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 82.8% on time across 169 flights, 4 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 4 points of difference.

One caution: this is a thin sample. 169 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 ONT

Put together: treat all of this as provisional. 169 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 78.4% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 167 completed flights over 12 months sit behind that.

Where to go next

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.

Key figures