Airport month record

IADAUG

Washington Dulles International in August 2025

Departures: 5,201
Month: August 2025
National, same month: 77.4%
Carriers: 10

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

IAD in August lands a B+, 4 points better than the national rate of 77.4%. 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 is a workable record, not a spotless one. That rests on 5,201 flights, of which Republic Airways flew 1,016 at 84.5% on time.

On time

81.0%

Arrivals under 15 minutes late, of 5,141 completed departures

Avg delay

70 min

Across delayed arrivals only, not all flights

Cancelled

0.79%

Nationally in August: 1.08%

Whole year

81.1%

IAD across all twelve months

These figures cover 5,201 departures from Washington Dulles International in August 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

August next to IAD's other months

Against IAD's own year, August ran level with the twelve-month rate of 81.1%, which makes it number eight of twelve months, best first. Cancellations were unusually low for IAD in August, at 0.79% against 1.37% across the year. Either side of it, July ran 69.5% on time and September 86.8%, 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 (this page)	5,201	81.0%	70 min	0.79%	B+
September 2025	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 August

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 19 points, against 3 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am494 flights90.1%
8am–11am1,307 flights86.7%
11am–2pm938 flights86.8%
2pm–5pm343 flights80.4%
5pm–8pm1,348 flights71.3%
8pm–5am771 flights75.5%

Scale runs 65% to 95%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 90.1% of the time, against 71.3% for the evening window. That is 19 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 1,348 flights scheduled in it.

Across the week, Tuesday is the strongest day at 86.5% on time and Wednesday the weakest at 78.2%. 8 points is a smaller lever than departure hour, but it is free.

Carrier by carrier

Which airlines ran best at IAD in August

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 August 2025
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	2,988	81.6%	64 min	0.60%	B+
Republic Airways	1,016	84.5%	64 min	0.98%	B+
Delta Air Linesthin sample	251	81.0%	100 min	0.80%	B+
SkyWest Airlinesthin sample	204	80.2%	106 min	0.00%	B+
Alaska Airlinesthin sample	181	77.2%	40 min	0.55%	B+
Frontier Airlinesthin sample	175	62.4%	103 min	1.14%	D
Southwest Airlinesthin sample	113	72.3%	62 min	0.00%	C+
PSA Airlinesthin sample	105	83.3%	69 min	2.86%	B
American Airlinesthin sample	100	77.4%	80 min	5.00%	B−
Allegiant Airthin sample	68	76.5%	89 min	0.00%	B+

No carrier stands out. Republic tops the table at 84.5%, 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 August

Routes from IAD in August 2025
Route	Flights	On time	Avg delay	Cancelled	Grade
IAD to ATL · Atlantathin sample	343	77.3%	83 min	0.58%	B+
IAD to DEN · Denverthin sample	335	76.2%	66 min	0.30%	B+
IAD to SFO · San Franciscothin sample	255	83.3%	73 min	1.18%	B
IAD to SEA · Seattlethin sample	221	80.5%	64 min	0.45%	B+
IAD to LAX · Los Angelesthin sample	196	79.0%	60 min	0.51%	B+
IAD to ORD · Chicagothin sample	196	76.0%	70 min	1.02%	B
IAD to MCO · Orlandothin sample	178	70.5%	78 min	0.56%	C+
IAD to IAH · Houstonthin sample	174	79.3%	41 min	0.00%	B+
IAD to DFW · Dallas-Fort Worththin sample	166	79.0%	77 min	3.61%	B−
IAD to CLT · Charlottethin sample	162	83.0%	78 min	1.85%	B
IAD to BOS · Bostonthin sample	134	79.9%	61 min	0.00%	B+
IAD to TPA · Tampathin sample	129	76.4%	47 min	0.78%	B+
IAD to SAN · San Diegothin sample	124	91.1%	61 min	0.81%	A+
IAD to EWR · Newarkthin sample	124	60.2%	96 min	0.81%	D+
IAD to LAS · Las Vegasthin sample	119	79.7%	69 min	0.00%	B+
IAD to CMH · Columbusthin sample	109	86.2%	47 min	0.00%	A+
IAD to PWM · Portlandthin sample	108	91.6%	39 min	0.93%	A+
IAD to LGA · New Yorkthin sample	107	79.6%	76 min	3.74%	B−
IAD to RDU · Raleighthin sample	107	86.8%	51 min	0.93%	A+
IAD to PIT · Pittsburghthin sample	105	84.6%	51 min	0.95%	B+
IAD to AUS · Austinthin sample	102	85.0%	42 min	1.96%	A
IAD to BNA · Nashvillethin sample	100	84.0%	77 min	0.00%	B+
IAD to IND · Indianapolisthin sample	93	81.7%	50 min	0.00%	B+
IAD to CLE · Clevelandthin sample	90	84.3%	46 min	1.11%	B
IAD to PHX · Phoenixthin sample	88	83.9%	58 min	0.00%	B+

Delay causes

What held IAD 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 68,000 reported delay minutes.

Late-arriving aircraft
39%
Carrier
34%
National Airspace System
24%
Extreme weather
4%
Security
0%

39% 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 68,000 reported delay minutes here, that single category outweighs weather by 11 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 68,055 reported delay minutes.

Cancellations are rare at 0.79%, below the national 1.08% 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.

6.2% of arrivals land an hour or more late, close to the national 8.2%. 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 a little over an hour, which a normal layover absorbs.

What to do with this

Flying from IAD in August

For a August trip through IAD: expect 81.0% on time and 0.79% cancelled, going by August 2025. The 5am–8am window was the strongest part of the day.

Washington Dulles International (IAD), the whole year
IAD in July69.5%
IAD in September86.8%
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