Airport month record

ONTDEC

Ontario International in December 2025

Departures: 2,132
Month: December 2025
National, same month: 73.2%
Carriers: 7

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

ONT in December lands a B+, 9 points better than the national rate of 73.2%. About one flight in six arrives 15 minutes late or worse, and those flights are late by a little over an hour on average. That rests on 2,132 flights, with a median arrival 6 minutes early.

Set against the rest of the country, ONT's December record is 9 points better than the US average of 73.2%. That gap is worth roughly 92 fewer late arrivals for every thousand flights.

On time

82.4%

Arrivals under 15 minutes late, of 2,115 completed departures

Avg delay

70 min

Across delayed arrivals only, not all flights

Cancelled

0.70%

Nationally in December: 1.55%

Whole year

81.9%

ONT across all twelve months

These figures cover 2,132 departures from Ontario International in December 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

December next to ONT's other months

Against ONT's own year, December ran level with the twelve-month rate of 81.9%, which makes it number six of twelve months, best first. Either side of it, November ran 81.9% on time and January 86.5%, 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 (this page)	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 December

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 20 points, against half a point between the best and worst carrier.

5am–8am625 flights91.9%
8am–11am335 flights86.4%
11am–2pm395 flights75.5%
2pm–5pm325 flights75.5%
5pm–8pm284 flights71.7%
8pm–5am168 flights86.0%

Scale runs 65% to 95%.

Book the early departure. Flights leaving between 5am–8am arrive on time 91.9% of the time, against 71.7% for the evening window. That is 20 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 625 flights scheduled in it.

Across the week, Tuesday is the strongest day at 84.7% on time and Friday the weakest at 78.4%, a spread of 6 points.

Carrier by carrier

Which airlines ran best at ONT in December

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 December 2025
Airline	Flights	On time	Avg delay	Cancelled	Grade
Southwest Airlines	1,005	82.1%	46 min	0.30%	B+
American Airlinesthin sample	336	81.8%	120 min	0.00%	B+
United Airlinesthin sample	171	81.9%	90 min	0.00%	B+
Alaska Airlinesthin sample	169	85.0%	50 min	1.18%	A
Frontier Airlinesthin sample	157	76.3%	98 min	3.18%	B−
Delta Air Linesthin sample	147	88.1%	87 min	2.72%	A
SkyWest Airlinesthin sample	147	83.4%	71 min	0.68%	B+

Route by route

Busiest routes out of ONT in December

Routes from ONT in December 2025
Route	Flights	On time	Avg delay	Cancelled	Grade
ONT to PHX · Phoenixthin sample	282	80.1%	77 min	0.00%	B+
ONT to LAS · Las Vegasthin sample	206	84.3%	87 min	0.97%	B+
ONT to DFW · Dallas-Fort Worththin sample	201	81.8%	119 min	1.49%	B
ONT to SEA · Seattlethin sample	200	81.7%	65 min	1.00%	B
ONT to DEN · Denverthin sample	195	77.3%	71 min	0.00%	B+
ONT to SMF · Sacramentothin sample	179	85.5%	52 min	0.00%	A+
ONT to OAK · Oaklandthin sample	121	79.3%	51 min	0.00%	B+
ONT to SJC · San Josethin sample	118	90.6%	34 min	0.85%	A+
ONT to SFO · San Franciscothin sample	104	75.5%	75 min	1.92%	B
ONT to SLC · Salt Lake Citythin sample	90	85.6%	81 min	0.00%	A+
ONT to ATL · Atlantathin sample	88	89.3%	93 min	4.55%	A−
ONT to PDX · Portlandthin sample	44	88.6%	60 min	0.00%	A+
ONT to IAH · Houstonthin sample	44	77.3%	43 min	0.00%	B+
ONT to DAL · Dallasthin sample	42	85.7%	33 min	0.00%	A+
ONT to HNL · Honoluluthin sample	31	93.5%	37 min	0.00%	A+
ONT to CLT · Charlottethin sample	31	87.1%	24 min	0.00%	A+
ONT to AUS · Austinthin sample	31	76.7%	39 min	3.23%	B−
ONT to BNA · Nashvillethin sample	31	83.9%	28 min	0.00%	B+
ONT to HOU · Houstonthin sample	31	64.5%	57 min	0.00%	D+
ONT to MDW · Chicagothin sample	31	87.1%	40 min	0.00%	A+

Delay causes

What held ONT up in December

Late-arriving aircraft accounts for 46% of the 26,000 delay minutes carriers reported here, and the remaining four split what is left.

Late-arriving aircraft
46%
Carrier
37%
National Airspace System
15%
Extreme weather
2%
Security
0%

46% 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 29 to one. The split is drawn from 26,225 reported delay minutes.

Cancellations are rare at 0.70%, below the national 1.55% 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.

5.5% of arrivals land an hour or more late, close to the national 10.0%, 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 December

For a December trip through ONT: expect 82.4% on time and 0.70% cancelled, going by December 2025. 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 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