Carrier route record

F9SFO→ONT

Frontier Airlines · San Francisco to Ontario

Flights: 177
Period: July 2025 to June 2026
Share of route: 14%
Carriers: 3

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

Frontier on SFO to ONT earns a D−, which is as low as this site's scale goes for a reason. Only 56.7% of flights arrive inside the 15-minute window, 21 points worse than the national rate of 77.6%. Late arrivals average close to two hours. Treat any tight connection here as a coin flip. That rests on 177 flights, with a median arrival 7 minutes late.

The national on-time rate over the same period is 77.6%, so Frontier on SFO to ONT runs 21 points behind the country as a whole. Across a thousand flights that is about 209 extra late arrivals.

On time

56.7%

Arrivals under 15 minutes late, of 171 completed flights

Avg delay

107 min

Across delayed arrivals only, not all flights

Cancelled

3.39%

National rate is 1.81%

Whole route

76.8%

Every carrier on SFO to ONT, 1,291 flights

These figures cover 177 flights between July 2025 and June 2026. Beyond the headline rate, 19.9% 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 SFO to ONT

Frontier flew 177 of the 1,291 flights on SFO to ONT, about 14% of it. Its 56.7% on time is 20 points worse than the route as a whole, which runs 76.8%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from United at 81.0% to Frontier at 56.7%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.

On-time performance by carrier on SFO to ONT
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	1,008	81.0%	55 min	0.30%	B+
SkyWest Airlinesthin sample	106	68.9%	77 min	2.83%	C
Frontier Airlines (this page)thin sample	177	56.7%	107 min	3.39%	D−

Departure window

When Frontier runs best on this route

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 30 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am—
8am–11am59 flights77.2%
11am–2pm11 flights—
2pm–5pm—
5pm–8pm1 flights—
8pm–5am106 flights47.1%

Scale runs 40% to 85%. Rows with fewer than 30 flights show a dash.

The 8pm–5am window is where this operation falls apart: 47.1% on time, against 77.2% for the 8am–11am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 8pm–5am window is the busiest, with 106 flights scheduled in it.

Across the year

Frontier on SFO to ONT through the year

Jul–Sep 202545 flights45.5%
Oct–Dec 202554 flights45.3%
Jan–Mar 202615 flights—
Apr–Jun 202663 flights67.2%

Scale runs 35% to 75%. 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 56.7% on time across 177 flights.

Frontier on SFO to ONT did not run the same all year. Its best quarter was Apr–Jun 2026 at 67.2% on time and its weakest Oct–Dec 2025 at 45.3%, a swing of 22 points on roughly 59 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, Monday is the strongest day at 59.5% on time and Sunday the weakest at 48.6%. 11 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. Late-arriving aircraft accounts for 64% of the 7,924 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.

Late-arriving aircraft
64%
Carrier
34%
National Airspace System
2%

64% 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 7,924 reported delay minutes here, that single category outweighs weather by 64 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 7,924 reported delay minutes.

The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 77.2% on time here.

Cancellations run at 3.39%, against 1.81% nationally. That is about one flight in 30 cancelled outright. A cancelled flight is invisible in every on-time figure on this page, so the punctuality numbers above describe only the flights that actually operated.

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. 19.9% 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.

At 363 miles this is a short hop, and stage length matters more than it looks. A flight this short spends under two hours in the air, which leaves almost nothing to claw back a late pushback with. Delay here is decided on the ground, in the turn, which is why the 8am–11am window matters as much as it does.

The return leg is a different operation and performs like one: it runs 41.6% on time across 177 flights, 15 points below 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 15 points of difference.

One caution: this is a thin sample. 177 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 SFO to ONT

Put together: the delay figures matter less here than the 3.39% cancellation rate. A late arrival costs you close to two hours; a cancelled flight costs you the day. Book the 8am–11am departure so there is still a schedule behind you if it goes wrong, and treat a same-day connection as optimistic. 171 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