Airport month record

ONTMAY

Ontario International in May 2026

Departures: 2,298
Month: May 2026
National, same month: 78.6%
Carriers: 7

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

ONT in May lands a B+, about a point better than the national rate of 78.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 2,298 flights, with a median arrival 8 minutes early.

On time

80.0%

Arrivals under 15 minutes late, of 2,279 completed departures

Avg delay

58 min

Across delayed arrivals only, not all flights

Cancelled

0.70%

Nationally in May: 0.92%

Whole year

81.9%

ONT across all twelve months

These figures cover 2,298 departures from Ontario International in May 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

May next to ONT's other months

Against ONT's own year, May ran 2 points worse than the twelve-month rate of 81.9%, which makes it number ten of twelve months, best first. Either side of it, April ran 82.8% on time and June 76.7%, so this month sits in line with its neighbours.

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 (this page)	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 May

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 26 points, against half a point between the best and worst carrier.

5am–8am568 flights94.3%
8am–11am368 flights82.4%
11am–2pm488 flights76.9%
2pm–5pm300 flights68.0%
5pm–8pm281 flights68.8%
8pm–5am293 flights77.2%

Scale runs 60% to 100%.

Book the early departure. Flights leaving between 5am–8am arrive on time 94.3% of the time, against 68.0% for the afternoon window. That is 26 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 568 flights scheduled in it.

Across the week, Saturday is the strongest day at 88.6% on time and Friday the weakest at 77.4%, a spread of 11 points.

Carrier by carrier

Which airlines ran best at ONT in May

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 May 2026
Airline	Flights	On time	Avg delay	Cancelled	Grade
Southwest Airlines	992	75.6%	47 min	0.30%	B+
American Airlinesthin sample	291	86.8%	77 min	2.41%	A
United Airlinesthin sample	228	72.8%	62 min	0.00%	C+
Frontier Airlinesthin sample	209	75.5%	83 min	0.48%	B+
SkyWest Airlinesthin sample	186	88.1%	49 min	0.54%	A+
Alaska Airlinesthin sample	178	88.1%	53 min	1.12%	A
Delta Air Linesthin sample	175	91.3%	66 min	1.14%	A

Route by route

Busiest routes out of ONT in May

Routes from ONT in May 2026
Route	Flights	On time	Avg delay	Cancelled	Grade
ONT to PHX · Phoenixthin sample	254	87.8%	47 min	0.00%	A+
ONT to SEA · Seattlethin sample	249	89.1%	85 min	0.80%	A+
ONT to DEN · Denverthin sample	242	83.9%	58 min	0.00%	B+
ONT to LAS · Las Vegasthin sample	199	64.3%	51 min	0.00%	D+
ONT to DFW · Dallas-Fort Worththin sample	197	82.4%	78 min	3.55%	B−
ONT to SMF · Sacramentothin sample	187	79.6%	51 min	0.53%	B+
ONT to SFO · San Franciscothin sample	127	43.2%	62 min	1.57%	F
ONT to OAK · Oaklandthin sample	118	80.5%	65 min	0.00%	B+
ONT to SLC · Salt Lake Citythin sample	115	96.5%	62 min	0.87%	A+
ONT to SJC · San Josethin sample	110	91.8%	29 min	0.00%	A+
ONT to ATL · Atlantathin sample	93	87.0%	64 min	1.08%	A
ONT to IAH · Houstonthin sample	61	83.6%	83 min	0.00%	B+
ONT to PDX · Portlandthin sample	38	89.5%	40 min	0.00%	A+
ONT to DAL · Dallasthin sample	35	54.5%	34 min	5.71%	F−
ONT to ORD · Chicagothin sample	31	74.2%	60 min	0.00%	C+
ONT to HNL · Honoluluthin sample	31	96.8%	29 min	0.00%	A+
ONT to CLT · Charlottethin sample	31	90.3%	38 min	0.00%	A+
ONT to BNA · Nashvillethin sample	31	48.4%	42 min	0.00%	F+
ONT to BWI · Baltimorethin sample	31	80.6%	36 min	0.00%	B+
ONT to HOU · Houstonthin sample	31	41.9%	33 min	0.00%	F+
ONT to MDW · Chicagothin sample	31	96.8%	49 min	0.00%	A+

Delay causes

What held ONT up in May

Late-arriving aircraft accounts for 43% of the 26,000 delay minutes carriers reported here, and the remaining four split what is left.

Late-arriving aircraft
43%
Carrier
28%
National Airspace System
28%
Extreme weather
1%
Security
0%

43% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 26,000 reported delay minutes here, that single category outweighs weather by 38 to one. The split is drawn from 26,220 reported delay minutes.

Cancellations are rare at 0.70%, below the national 0.92% 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.

5.7% of arrivals land an hour or more late, close to the national 7.1%, so a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last about an hour, which a normal layover absorbs.

What to do with this

Flying from ONT in May

For a May trip through ONT: plan on this being one of the airport's harder months. The 5am–8am departures held up best at 94.3% on time, and with 5.7% of arrivals an hour or more late, a connection here deserves more slack than the same trip in February would.

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 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