Route reliability record
ONT→SFO
Ontario to San Francisco
- Flights
- 1,290
- Period
- July 2025 to June 2026
- Distance
- 363 mi
- Carriers
- 3
This route draws a D+. About one flight in three arrives at least 15 minutes late, and the typical late arrival is about an hour behind schedule. Build slack into anything you connect to. That rests on 1,290 ONT to SFO flights, with a median arrival 1 minute late.
Best time to fly ONT to SFO: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 90.7% of the time and Tuesday flights 74.8%, against 64.9% for the route overall.
The national on-time rate over the same period is 77.6%, so this route runs 13 points behind the country as a whole. Across a thousand flights that is about 127 extra late arrivals.
Key figures
On time
64.9%
Arrivals under 15 minutes late, of 1,280 completed flights
Avg delay
67 min
Across delayed arrivals only, not all flights
Cancelled
0.78%
National rate is 1.81%
Best carrier
United
70.7% on time across 1,007 flights
These figures cover 1,290 flights between July 2025 and June 2026. Beyond the headline rate, 12.5% 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
Which airline is most reliable on ONT to SFO
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.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 1,007 | 70.7% | 66 min | 0.40% | C+ |
| SkyWest Airlinesthin sample | 106 | 48.1% | 68 min | 1.89% | F |
| Frontier Airlinesthin sample | 177 | 41.6% | 71 min | 2.26% | F |
Best ways to make this trip
The most reliable ways to fly Ontario to San Francisco
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. 5 of the top 5 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. LAX → SJCLos Angeles to San Jose | SkyWest Airlines | 91.1% | 91.4% | 0.34% | 8am–11am, Thu | OO 3883 18:00 |
| 2. LGB → OAKLong Beach to Oakland | Southwest Airlines | 89.1% | 89.4% | 0.31% | 5am–8am, Tue | — |
| 3. LGB → SJCLong Beach to San Jose | Southwest Airlines | 86.4% | 86.7% | 0.33% | 8am–11am, Wed | — |
| 4. ONT → OAKOntario to Oakland | Southwest Airlines | 86.0% | 86.3% | 0.40% | 5am–8am, Wed | — |
| 5. BUR → SJCBurbank to San Jose | Southwest Airlines | 85.8% | 86.8% | 1.10% | 5am–8am, Tue | — |
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 46 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–8am327 flights90.7%
- 8am–11am104 flights44.7%
- 11am–2pm231 flights72.7%
- 2pm–5pm140 flights65.7%
- 5pm–8pm335 flights49.4%
- 8pm–5am153 flights44.7%
Scale runs 35% to 95%. Rows with fewer than 30 flights show a dash.
The 8pm–5am window is where this operation falls apart: 44.7% on time, against 90.7% for the 5am–8am 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 5pm–8pm window is the busiest, with 335 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 58 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.
June is the worst month at 33.3% on time, 58 points below March, 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. May was the busiest month here, with 127 flights.
Across the week, Tuesday is the strongest day at 74.8% on time and Monday the weakest at 57.8%. 17 points is a smaller lever than departure hour, but it is free.
Delay causes
Why this route gets delayed
One category carries most of the weight here. National Airspace System accounts for 57% of the 30,000 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.
- 57%National Airspace System
- 25%Late-arriving aircraft
- 15%Carrier
- 3%Extreme weather
57% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 17,000 minutes out of 30,000, against a national NAS share of 21%. The split is drawn from 30,250 reported delay minutes.
Cancellations are rare at 0.78%, below the national 1.81% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.
Connections and stage length
What a delay here actually costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 12.5% 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 5am–8am window matters as much as it does.
The return leg is a different operation and performs like one: it runs 76.8% on time across 1,291 flights, 12 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 12 points of difference.
The sample behind these figures is 1,290 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 SFO 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. March runs 91.1% on time and June 33.3%, a swing of 58 points. If the dates move at all, move them out of June before you think about anything else. 1,280 completed flights over 12 months sit behind that.
Common questions
ONT to SFO questions
How often is ONT to SFO delayed?
About one flight in three arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 35.1% of the 1,290 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
How reliable is ONT to SFO compared with the rest of the country?
64.9% of flights arrive on time here against a national 77.6%, a difference of 13 points against it. That is worth a D+ on this site's grading scale.
What time of day has the fewest delays on ONT to SFO?
The 5am–8am departure window is the strongest at 90.7% on time. The 8pm–5am window is the weakest at 44.7%, 46 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 June delays on ONT to SFO?
June is the weakest month at 33.3% on time, compared with 91.1% in March. Across the year that is 58 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
- SFO to ONT — the return legseparate record
- San Francisco International (SFO) delay statistics
- United Airlines on ONT to SFO70.7%
- SkyWest Airlines on ONT to SFO48.1%
- Frontier Airlines on ONT to SFO41.6%
- ONT to PHX, a related route82.7%
- LAX to SFO, a related route64.8%
- ONT to DEN, a related route79.7%
- United Airlines on-time record70.7%
- SkyWest Airlines on-time record48.1%
- Frontier Airlines on-time record41.6%
- The best time of day to fly, according to 7.04 million flight records
- How often a connection fails at the major US hubs
Direction matters. ONT to SFO and SFO to ONT are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
Embed ONT to SFO’s on-time badge on your site
Paste this into a web page. The badge shows the current on-time rate, cancellation rate and grade, and updates every month. Preview it, or build a badge for another route or airport.
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.