Airport month record

ONTSEP

Ontario International in September 2025

Departures: 2,177
Month: September 2025
National, same month: 83.4%
Carriers: 8

Historical statistics for September 2025, not live status or a forecast for this year’s September. For today’s conditions at ONT, see live FAA status.

ONT in September earns a B+. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it about a point better than the national rate of 83.4%. When something does go wrong the average delay runs a little over an hour. That rests on 2,177 flights, with a median arrival 8 minutes early.

On time

84.8%

Arrivals under 15 minutes late, of 2,163 completed departures

Avg delay

76 min

Across delayed arrivals only, not all flights

Cancelled

0.51%

Nationally in September: 0.51%

Whole year

81.9%

ONT across all twelve months

These figures cover 2,177 departures from Ontario International in September 2025. On time means an arrival less than 15 minutes after the scheduled gate time, the DOT's threshold, and the national comparison uses every US departure in the same month rather than the whole year.

Against the year

September next to ONT's other months

Against ONT's own year, September ran 3 points better than the twelve-month rate of 81.9%, which makes it number three of twelve months, best first. Cancellations were unusually low for ONT in September, at 0.51% against 0.87% across the year.

ONT month by month
Month	Flights	On time	Avg delay	Cancelled	Grade
September 2025 (this page)	2,177	84.8%	76 min	0.51%	B+
October 2025	2,265	81.6%	64 min	0.49%	B+
November 2025	2,184	81.9%	63 min	2.06%	B
December 2025	2,132	82.4%	70 min	0.70%	B+
January 2026	1,892	86.5%	87 min	1.69%	A
February 2026	1,734	87.8%	70 min	0.35%	A+
March 2026	2,081	82.8%	57 min	1.01%	B
April 2026	2,119	82.8%	61 min	0.28%	B+
May 2026	2,298	80.0%	58 min	0.70%	B+
June 2026	2,304	76.7%	66 min	1.00%	B
July 2026	2,377	77.9%	75 min	0.88%	B+
August 2026	2,228	80.9%	70 min	0.81%	B+

Departure window

The best time of day to leave ONT in September

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 18 points, against half a point between the best and worst carrier.

5am–8am534 flights93.8%
8am–11am352 flights90.9%
11am–2pm462 flights84.8%
2pm–5pm300 flights76.8%
5pm–8pm287 flights75.6%
8pm–5am242 flights76.9%

Scale runs 65% to 100%.

Book the early departure. Flights leaving between 5am–8am arrive on time 93.8% of the time, against 75.6% for the evening window. That is 18 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 534 flights scheduled in it.

Across the week, Wednesday is the strongest day at 90.6% on time and Thursday the weakest at 80.2%, a spread of 10 points.

Carrier by carrier

Which airlines ran best at ONT in September

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.

Carriers at ONT in September 2025
Airline	Flights	On time	Avg delay	Cancelled	Grade
Southwest Airlines	966	86.3%	68 min	0.10%	A+
American Airlinesthin sample	261	82.5%	94 min	3.07%	B−
United Airlinesthin sample	232	80.1%	53 min	0.00%	B+
Frontier Airlinesthin sample	201	73.6%	74 min	0.00%	C+
Delta Air Linesthin sample	168	95.2%	139 min	0.00%	A+
SkyWest Airlinesthin sample	166	90.9%	136 min	0.60%	A+
Alaska Airlinesthin sample	153	84.9%	50 min	0.65%	B+
JetBlue Airwaysthin sample	30	73.3%	168 min	0.00%	C+

Route by route

Busiest routes out of ONT in September

Routes from ONT in September 2025
Route	Flights	On time	Avg delay	Cancelled	Grade
ONT to DEN · Denverthin sample	237	81.0%	66 min	0.00%	B+
ONT to PHX · Phoenixthin sample	227	85.6%	79 min	2.20%	A
ONT to SEA · Seattlethin sample	213	88.2%	62 min	0.47%	A+
ONT to LAS · Las Vegasthin sample	201	76.6%	83 min	0.00%	B+
ONT to DFW · Dallas-Fort Worththin sample	183	76.3%	77 min	2.73%	B
ONT to SMF · Sacramentothin sample	177	93.2%	56 min	0.00%	A+
ONT to OAK · Oaklandthin sample	133	91.0%	66 min	0.00%	A+
ONT to SLC · Salt Lake Citythin sample	110	90.9%	194 min	0.00%	A+
ONT to SFO · San Franciscothin sample	108	64.8%	52 min	0.00%	D+
ONT to SJC · San Josethin sample	107	86.0%	76 min	0.00%	A+
ONT to ATL · Atlantathin sample	77	97.4%	75 min	0.00%	A+
ONT to PDX · Portlandthin sample	61	91.8%	34 min	0.00%	A+
ONT to IAH · Houstonthin sample	43	83.7%	100 min	0.00%	B+
ONT to DAL · Dallasthin sample	34	82.4%	55 min	0.00%	B+
ONT to BNA · Nashvillethin sample	30	90.0%	28 min	0.00%	A+
ONT to BWI · Baltimorethin sample	30	80.0%	65 min	0.00%	B+
ONT to HOU · Houstonthin sample	30	96.7%	15 min	0.00%	A+
ONT to MDW · Chicagothin sample	30	96.7%	31 min	0.00%	A+
ONT to CLT · Charlottethin sample	30	93.3%	233 min	0.00%	A+
ONT to JFK · New Yorkthin sample	30	73.3%	168 min	0.00%	C+
ONT to HNL · Honoluluthin sample	30	86.7%	100 min	0.00%	A+
ONT to ORD · Chicagothin sample	30	86.2%	56 min	0.00%	A+

Delay causes

What held ONT up in September

Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 25,000 reported delay minutes.

Carrier
37%
Late-arriving aircraft
36%
National Airspace System
25%
Extreme weather
1%
Security
1%

36% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 25,000 reported delay minutes here, that single category outweighs weather by 36 to one. The split is drawn from 25,122 reported delay minutes.

Cancellations are rare at 0.51%, below the national 0.51% 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.

5.4% of arrivals land an hour or more late, close to the national 5.4%, so a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last a little over an hour, which a normal layover absorbs.

What to do with this

Flying from ONT in September

For a September trip through ONT: this is one of the better months to be flying from here, 84.8% on time with 0.51% cancelled. That is a base rate for the month as a whole; a single storm can still spoil a particular day.

Ontario International (ONT), the whole year
ONT in October81.6%
ONT in November81.9%
ONT in December82.4%
ONT in January86.5%
ONT in February87.8%
ONT in March82.8%
ONT in April82.8%
ONT in May80.0%
ONT in June76.7%
ONT in July77.9%
ONT in August80.9%

Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated 22 October 2026; recomputed monthly. How this data is collected.

Key figures