Airport month record

IADSEP

Washington Dulles International in September 2025

Departures: 4,815
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 IAD, see live FAA status.

IAD in September earns an A+. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 3 points better than the national rate of 83.4%. When something does go wrong the average delay runs about an hour. That rests on 4,815 flights, of which Republic Airways flew 834 at 88.6% on time.

On time

86.8%

Arrivals under 15 minutes late, of 4,793 completed departures

Avg delay

67 min

Across delayed arrivals only, not all flights

Cancelled

0.27%

Nationally in September: 0.51%

Whole year

81.1%

IAD across all twelve months

These figures cover 4,815 departures from Washington Dulles 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 IAD's other months

Against IAD's own year, September ran 6 points better than the twelve-month rate of 81.1%, which makes it number two of twelve months, best first. Cancellations were unusually low for IAD in September, at 0.27% against 1.37% across the year. Either side of it, August ran 81.0% on time and October 84.6%, so a trip moved by a few weeks would have landed in a worse stretch.

IAD month by month
Month	Flights	On time	Avg delay	Cancelled	Grade
July 2025	5,248	69.5%	102 min	2.88%	C
August 2025	5,201	81.0%	70 min	0.79%	B+
September 2025 (this page)	4,815	86.8%	67 min	0.27%	A+
October 2025	4,854	84.6%	64 min	0.27%	B+
November 2025	4,589	81.8%	71 min	1.46%	B
December 2025	4,676	74.8%	69 min	0.71%	C+
January 2026	4,248	83.0%	82 min	5.65%	B−
February 2026	4,037	83.3%	74 min	1.34%	B
March 2026	4,983	79.6%	92 min	1.81%	B
April 2026	4,843	87.2%	71 min	0.31%	A+
May 2026	5,474	84.1%	78 min	0.57%	B+
June 2026	5,053	78.1%	85 min	0.93%	B+

Departure window

The best time of day to leave IAD in September

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 16 points, against 3 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am397 flights93.9%
8am–11am1,089 flights92.8%
11am–2pm974 flights90.3%
2pm–5pm411 flights80.3%
5pm–8pm1,345 flights78.0%
8pm–5am599 flights89.1%

Scale runs 70% to 100%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 93.9% of the time, against 78.0% for the evening window. That is 16 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 1,345 flights scheduled in it.

Across the week, Tuesday is the strongest day at 92.1% on time and Thursday the weakest at 80.2%. 12 points is a smaller lever than departure hour, but it is free.

Carrier by carrier

Which airlines ran best at IAD in September

The two carriers here are closely matched: 3 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.

Carriers at IAD in September 2025
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	3,004	86.0%	59 min	0.13%	A+
Republic Airways	834	88.6%	73 min	0.72%	A+
Delta Air Linesthin sample	239	87.0%	78 min	0.00%	A+
SkyWest Airlinesthin sample	158	89.9%	155 min	0.00%	A+
Frontier Airlinesthin sample	124	91.1%	100 min	0.00%	A+
Alaska Airlinesthin sample	120	87.4%	37 min	0.00%	A+
PSA Airlinesthin sample	115	93.9%	64 min	0.87%	A+
Southwest Airlinesthin sample	112	76.6%	42 min	0.00%	B+
American Airlinesthin sample	90	85.1%	202 min	2.22%	A

No carrier stands out. Republic tops the table at 88.6%, 3 points clear of the bottom, which is inside the range this kind of sample moves year to year.

Route by route

Busiest routes out of IAD in September

Routes from IAD in September 2025
Route	Flights	On time	Avg delay	Cancelled	Grade
IAD to ATL · Atlantathin sample	315	88.2%	87 min	0.00%	A+
IAD to DEN · Denverthin sample	294	85.0%	46 min	0.00%	A+
IAD to SFO · San Franciscothin sample	206	87.4%	70 min	0.00%	A+
IAD to ORD · Chicagothin sample	203	78.8%	43 min	0.00%	B+
IAD to IAH · Houstonthin sample	195	92.3%	41 min	0.00%	A+
IAD to DFW · Dallas-Fort Worththin sample	185	84.0%	136 min	1.08%	B
IAD to SEA · Seattlethin sample	179	92.2%	45 min	0.00%	A+
IAD to LAX · Los Angelesthin sample	174	90.2%	46 min	0.57%	A+
IAD to MCO · Orlandothin sample	171	90.6%	60 min	0.00%	A+
IAD to CLT · Charlottethin sample	164	94.5%	72 min	0.61%	A+
IAD to BOS · Bostonthin sample	142	57.9%	67 min	1.41%	D
IAD to RDU · Raleighthin sample	140	87.8%	58 min	0.71%	A+
IAD to CMH · Columbusthin sample	136	82.4%	80 min	0.00%	B+
IAD to TPA · Tampathin sample	122	81.1%	46 min	0.00%	B+
IAD to EWR · Newarkthin sample	122	71.3%	79 min	0.00%	C+
IAD to SAN · San Diegothin sample	119	89.7%	32 min	0.00%	A+
IAD to LGA · New Yorkthin sample	111	82.2%	52 min	3.60%	B−
IAD to PIT · Pittsburghthin sample	111	90.1%	55 min	0.00%	A+
IAD to AUS · Austinthin sample	109	92.7%	64 min	0.00%	A+
IAD to BDL · Hartfordthin sample	107	87.9%	38 min	0.00%	A+
IAD to CLE · Clevelandthin sample	97	86.6%	85 min	0.00%	A+
IAD to PWM · Portlandthin sample	94	92.5%	58 min	1.06%	A
IAD to LAS · Las Vegasthin sample	91	91.2%	60 min	0.00%	A+
IAD to IND · Indianapolisthin sample	89	87.6%	54 min	0.00%	A+
IAD to PHX · Phoenixthin sample	87	75.6%	34 min	0.00%	B+

Delay causes

What held IAD 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 43,000 reported delay minutes.

Late-arriving aircraft
36%
Carrier
33%
National Airspace System
29%
Extreme weather
2%

36% 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 43,000 reported delay minutes here, that single category outweighs weather by 15 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 42,591 reported delay minutes.

Cancellations are rare at 0.27%, 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.

Badly late arrivals are rare here: only 4.0% land an hour or more behind schedule, against 5.4% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.

What to do with this

Flying from IAD in September

For a September trip through IAD: this is one of the better months to be flying from here, 86.8% on time with 0.27% cancelled. That is a base rate for the month as a whole; a single storm can still spoil a particular day.

Washington Dulles International (IAD), the whole year
IAD in July69.5%
IAD in August81.0%
IAD in October84.6%
IAD in November81.8%
IAD in December74.8%
IAD in January83.0%
IAD in February83.3%
IAD in March79.6%
IAD in April87.2%
IAD in May84.1%
IAD in June78.1%

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