Airport month record

DENSEP

Denver International in September 2025

Departures: 26,548
Month: September 2025
National, same month: 83.4%
Carriers: 9

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

DEN in September lands a B+, 4 points worse than the national rate of 83.4%. About one flight in five arrives 15 minutes late or worse, and those flights are late by roughly 55 minutes on average. That is a workable record, not a spotless one. That rests on 26,548 flights, of which Delta Air Lines flew 991 at 87.6% on time.

Delta Air Lines is the most reliable of the six carriers covered here at 87.6% on time across 991 flights.

On time

79.4%

Arrivals under 15 minutes late, of 26,467 completed departures

Avg delay

54 min

Across delayed arrivals only, not all flights

Cancelled

0.12%

Nationally in September: 0.51%

Whole year

76.3%

DEN across all twelve months

These figures cover 26,548 departures from Denver 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 DEN's other months

Against DEN's own year, September ran 3 points better than the twelve-month rate of 76.3%, which makes it number six of twelve months, best first. Cancellations were unusually low for DEN in September, at 0.12% against 0.79% across the year. Either side of it, August ran 70.1% on time and October 80.8%, so a trip moved by a few weeks would have landed in a worse stretch.

DEN month by month
Month	Flights	On time	Avg delay	Cancelled	Grade
July 2025	29,433	63.0%	77 min	1.48%	D
August 2025	28,084	70.1%	69 min	0.73%	C+
September 2025 (this page)	26,548	79.4%	54 min	0.12%	B+
October 2025	27,763	80.8%	52 min	0.13%	B+
November 2025	25,280	84.7%	62 min	1.44%	B
December 2025	26,026	74.3%	68 min	0.64%	C+
January 2026	24,484	82.3%	60 min	1.69%	B
February 2026	23,046	82.4%	69 min	0.88%	B+
March 2026	27,089	76.8%	72 min	1.50%	B
April 2026	25,345	82.5%	56 min	0.27%	B+
May 2026	27,406	76.4%	58 min	0.28%	B+
June 2026	28,634	67.1%	64 min	0.41%	C+

Departure window

The best time of day to leave DEN in September

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 26 points, against 15 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am1,785 flights94.2%
8am–11am5,670 flights86.0%
11am–2pm5,741 flights84.8%
2pm–5pm4,240 flights77.2%
5pm–8pm5,881 flights68.1%
8pm–5am3,231 flights73.6%

Scale runs 60% to 100%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 94.2% of the time, against 68.1% for the evening 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 5pm–8pm window is the busiest, with 5,881 flights scheduled in it.

Across the week, Wednesday is the strongest day at 87.8% on time and Thursday the weakest at 71.9%. 16 points is a smaller lever than departure hour, but it is free.

Carrier by carrier

Which airlines ran best at DEN in September

The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 87.6% of the time; Southwest Airlines manages 72.6%. Sample sizes sit next to every figure, because a two-point gap across 7,301 flights means less than a ten-point one.

Carriers at DEN in September 2025
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	8,932	80.5%	53 min	0.11%	B+
Southwest Airlines	7,301	72.6%	48 min	0.14%	C+
SkyWest Airlines	6,403	84.6%	56 min	0.05%	B+
Frontier Airlines	1,864	77.9%	63 min	0.05%	B+
Delta Air Lines	991	87.6%	66 min	0.00%	A+
American Airlines	725	81.2%	81 min	1.10%	B
Alaska Airlinesthin sample	200	79.5%	49 min	0.00%	B+
JetBlue Airwaysthin sample	82	72.8%	101 min	1.22%	C
Allegiant Airthin sample	42	85.7%	64 min	0.00%	A+

The spread between Delta and Southwest is 15 points, wide enough that it should decide the booking. On a hundred trips that is 15 more arrivals inside the on-time window.

Route by route

Busiest routes out of DEN in September

Routes from DEN in September 2025
Route	Flights	On time	Avg delay	Cancelled	Grade
DEN to PHX · Phoenix	665	77.3%	70 min	1.05%	B
DEN to LAX · Los Angeles	650	83.2%	51 min	0.15%	B+
DEN to SLC · Salt Lake City	644	82.1%	52 min	0.00%	B+
DEN to ORD · Chicago	604	77.6%	50 min	0.00%	B+
DEN to SEA · Seattle	575	78.6%	48 min	0.00%	B+
DEN to LAS · Las Vegas	537	71.2%	60 min	0.19%	C+
DEN to MSP · Minneapolis	527	77.7%	54 min	0.00%	B+
DEN to DFW · Dallas-Fort Worth	463	79.7%	67 min	1.51%	B
DEN to SFO · San Francisco	451	74.3%	47 min	0.00%	C+
DEN to ATL · Atlanta	450	84.9%	52 min	0.00%	B+
DEN to COS · Colorado Springs	443	79.0%	55 min	0.00%	B+
DEN to SAN · San Diego	411	72.7%	69 min	0.73%	C+
DEN to LGA · New York	399	75.9%	52 min	0.00%	B+
DEN to PDX · Portland	395	82.0%	47 min	0.00%	B+
DEN to IAH · Houston	382	81.4%	53 min	0.26%	B+
DEN to AUS · Austin	378	77.5%	56 min	0.00%	B+
DEN to MCI · Kansas Citythin sample	361	73.1%	49 min	0.00%	C+
DEN to SMF · Sacramentothin sample	344	76.2%	55 min	0.00%	B+
DEN to BOS · Bostonthin sample	333	51.4%	81 min	0.60%	F+
DEN to STL · St. Louisthin sample	326	83.7%	44 min	0.00%	B+
DEN to MCO · Orlandothin sample	318	81.4%	52 min	0.00%	B+
DEN to BNA · Nashvillethin sample	315	77.5%	42 min	0.00%	B+
DEN to SNA · Santa Anathin sample	314	80.5%	44 min	0.00%	B+
DEN to EWR · Newarkthin sample	296	73.4%	78 min	1.01%	C
DEN to IAD · Washingtonthin sample	292	79.1%	51 min	0.00%	B+

Delay causes

What held DEN up in September

One category carries most of the weight here. Late-arriving aircraft accounts for 43% of the 292,000 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.

Late-arriving aircraft
43%
Carrier
32%
National Airspace System
23%
Extreme weather
3%
Security
0%

43% 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 292,000 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 291,720 reported delay minutes.

Cancellations are rare at 0.12%, 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.

5.7% of arrivals land an hour or more late, close to the national 5.4%. 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.

What to do with this

Flying from DEN in September

For a September trip through DEN: expect 79.4% on time and 0.12% cancelled, going by September 2025. The 5am–8am window was the strongest part of the day.

Denver International (DEN), the whole year
DEN in July63.0%
DEN in August70.1%
DEN in October80.8%
DEN in November84.7%
DEN in December74.3%
DEN in January82.3%
DEN in February82.4%
DEN in March76.8%
DEN in April82.5%
DEN in May76.4%
DEN in June67.1%

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.

Key figures