Airport month record

ONTAUG

Ontario International in August 2026

Departures: 2,228
Month: August 2026
National, same month: 73.1%
Carriers: 8

Historical statistics for August 2026, not live status or a forecast for this year’s August. For today’s conditions at ONT, see live FAA status.

ONT in August lands a B+, 8 points better than the national rate of 73.1%. 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 rests on 2,228 flights, with a median arrival 7 minutes early.

Set against the rest of the country, ONT's August record is 8 points better than the US average of 73.1%. That gap is worth roughly 78 fewer late arrivals for every thousand flights.

On time

80.9%

Arrivals under 15 minutes late, of 2,202 completed departures

Avg delay

70 min

Across delayed arrivals only, not all flights

Cancelled

0.81%

Nationally in August: 1.86%

Whole year

81.9%

ONT across all twelve months

These figures cover 2,228 departures from Ontario International in August 2026. 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

August next to ONT's other months

Against ONT's own year, August ran about a point worse than the twelve-month rate of 81.9%, which makes it number nine of twelve months, best first.

ONT month by month
Month	Flights	On time	Avg delay	Cancelled	Grade
September 2025	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 (this page)	2,228	80.9%	70 min	0.81%	B+

Departure window

The best time of day to leave ONT in August

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 24 points, against half a point between the best and worst carrier.

5am–8am580 flights93.7%
8am–11am422 flights82.4%
11am–2pm449 flights77.8%
2pm–5pm377 flights69.9%
5pm–8pm212 flights75.7%
8pm–5am188 flights73.2%

Scale runs 60% to 100%.

Book the early departure. Flights leaving between 5am–8am arrive on time 93.7% of the time, against 69.9% for the afternoon window. That is 24 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 580 flights scheduled in it.

Across the week, Tuesday is the strongest day at 89.3% on time and Monday the weakest at 77.5%, a spread of 12 points.

Carrier by carrier

Which airlines ran best at ONT in August

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 August 2026
Airline	Flights	On time	Avg delay	Cancelled	Grade
Southwest Airlines	966	82.8%	59 min	0.52%	B+
Frontier Airlinesthin sample	248	72.3%	52 min	2.42%	C
American Airlinesthin sample	232	84.3%	141 min	0.00%	B+
United Airlinesthin sample	209	74.4%	69 min	0.00%	C+
SkyWest Airlinesthin sample	200	85.9%	61 min	0.00%	A+
Alaska Airlinesthin sample	200	79.4%	58 min	0.50%	B+
Delta Air Linesthin sample	142	89.3%	102 min	1.41%	A
JetBlue Airwaysthin sample	31	44.4%	123 min	12.90%	F−

Route by route

Busiest routes out of ONT in August

Routes from ONT in August 2026
Route	Flights	On time	Avg delay	Cancelled	Grade
ONT to SEA · Seattlethin sample	249	79.3%	64 min	1.20%	B
ONT to DEN · Denverthin sample	235	81.7%	77 min	0.85%	B+
ONT to PHX · Phoenixthin sample	221	83.0%	76 min	0.00%	B+
ONT to LAS · Las Vegasthin sample	196	70.5%	60 min	1.02%	C
ONT to DFW · Dallas-Fort Worththin sample	190	82.5%	117 min	0.53%	B+
ONT to SMF · Sacramentothin sample	183	86.8%	48 min	0.55%	A+
ONT to SFO · San Franciscothin sample	135	54.8%	57 min	0.00%	F+
ONT to SLC · Salt Lake Citythin sample	118	89.7%	72 min	0.85%	A+
ONT to OAK · Oaklandthin sample	114	84.8%	84 min	1.75%	B
ONT to SJC · San Josethin sample	111	92.8%	58 min	0.00%	A+
ONT to ATL · Atlantathin sample	79	92.3%	130 min	1.27%	A
ONT to HNL · Honoluluthin sample	54	75.9%	45 min	0.00%	B+
ONT to IAH · Houstonthin sample	53	88.5%	43 min	1.89%	A
ONT to PDX · Portlandthin sample	39	94.9%	21 min	0.00%	A+
ONT to DAL · Dallasthin sample	31	83.9%	95 min	0.00%	B+
ONT to ORD · Chicagothin sample	31	83.9%	114 min	0.00%	B+
ONT to STS · Santa Rosathin sample	31	96.7%	54 min	0.00%	A+
ONT to BNA · Nashvillethin sample	31	80.6%	25 min	0.00%	B+
ONT to HOU · Houstonthin sample	31	67.7%	30 min	0.00%	C+
ONT to MDW · Chicagothin sample	31	100.0%	—	0.00%	A+
ONT to JFK · New Yorkthin sample	31	44.4%	123 min	12.90%	F−

Delay causes

What held ONT up in August

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 29,000 reported delay minutes.

Late-arriving aircraft
39%
Carrier
30%
National Airspace System
30%
Extreme weather
1%
Security
0%

39% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 29,000 reported delay minutes here, that single category outweighs weather by 35 to one. The split is drawn from 29,134 reported delay minutes.

Cancellations are rare at 0.81%, below the national 1.86% 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.

6.6% of arrivals land an hour or more late, close to the national 10.9%, 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 August

For a August trip through ONT: expect 80.9% on time and 0.81% cancelled, going by August 2026. The 5am–8am window was the strongest part of the day.

Ontario International (ONT), the whole year
ONT in September84.8%
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%

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