Carrier route record
WNONT→DEN
Southwest Airlines · Ontario to Denver
- Flights
- 1,267
- Period
- July 2025 to June 2026
- Share of route
- 47%
- Carriers
- 3
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Southwest Airlines.
Southwest on ONT to DEN sits in the middle of the pack with a B+. Close to three flights in four arrive on time by the DOT's definition, 2 points worse than the national rate of 77.6%. The late ones land roughly 55 minutes behind schedule. That rests on 1,267 flights. The strongest carrier on the route with a full sample, United Airlines, flew 853 at 85.1% on time.
The US average over the same twelve months is 77.6%, so there is little to separate Southwest on ONT to DEN from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
75.9%
Arrivals under 15 minutes late, of 1,257 completed flights
Avg delay
53 min
Across delayed arrivals only, not all flights
Cancelled
0.39%
National rate is 1.81%
Whole route
79.7%
Every carrier on ONT to DEN, 2,672 flights
These figures cover 1,267 flights between July 2025 and June 2026. The median arrival is 2 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.
Carrier by carrier
Southwest against every carrier on ONT to DEN
Southwest flew 1,267 of the 2,672 flights on ONT to DEN, about 47% of it. Its 75.9% on time is 4 points worse than the route as a whole, which runs 79.7%. Ranked by on-time rate it is last of three carriers on the route, where the range runs from United at 85.1% to Southwest at 75.9%.
The two carriers here are closely matched: 5 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 853 | 85.1% | 85 min | 0.35% | A+ |
| Frontier Airlines | 552 | 80.1% | 98 min | 0.72% | B+ |
| Southwest Airlines (this page) | 1,267 | 75.9% | 53 min | 0.39% | B+ |
No carrier stands out. United tops the table at 85.1%, 5 points clear of the bottom, which is inside the range this kind of sample moves year to year.
Departure window
When Southwest runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 33 points, against 5 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am378 flights90.4%
- 8am–11am299 flights90.3%
- 11am–2pm220 flights62.7%
- 2pm–5pm364 flights57.7%
- 5pm–8pm6 flights—
- 8pm–5am—
Scale runs 50% to 95%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 90.4% of the time, against 57.7% for the afternoon window. That is 33 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5am–8am window is the busiest, with 378 flights scheduled in it.
Across the year
Southwest on ONT to DEN through the year
June is the worst month at 67.0% on time, 18 points below January, the best at 84.8%. 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 119 flights.
Across the week, Saturday is the strongest day at 81.5% on time and Friday the weakest at 72.5%. 9 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Southwest runs late on this route
One category carries most of the weight here. National Airspace System accounts for 44% of the 16,000 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.
- 44%National Airspace System
- 35%Late-arriving aircraft
- 18%Carrier
- 2%Extreme weather
- 1%Security
35% 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 16,000 reported delay minutes here, that single category outweighs weather by 16 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 15,926 reported delay minutes.
44% 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 7,081 minutes out of 16,000, against a national NAS share of 21%.
Cancellations are rare at 0.39%, 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 costs
7.1% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last roughly 55 minutes, which a normal layover absorbs.
The 819 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 68.0% on time across 1,267 flights, 8 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 8 points of difference.
The sample behind these figures is 1,267 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.
What to do with this
Booking Southwest on ONT to DEN
Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 84.8% on time and June 67.0%, a swing of 18 points. If the dates move at all, move them out of June before you think about anything else. 1,257 completed flights over 12 months sit behind that.
Related
Where to go next
- ONT to DEN, every carrier
- Southwest on DEN to ONT, the return leg
- United Airlines on ONT to DEN85.1%
- Frontier Airlines on ONT to DEN80.1%
- Southwest Airlines network-wide record
- Denver International (DEN) delay statistics
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.04 million flight records
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.