Airport month record
IADMAY
Washington Dulles International in May 2026
- Departures
- 5,474
- Month
- May 2026
- National, same month
- 78.6%
- Carriers
- 10
Historical statistics for May 2026, not live status or a forecast for this year’s May. For today’s conditions at IAD, see live FAA status.
IAD in May earns a B+. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 6 points better than the national rate of 78.6%. When something does go wrong the average delay runs a little over an hour. That rests on 5,474 flights, of which United Airlines flew 3,541 at 85.1% on time.
Set against the rest of the country, IAD's May record is 6 points better than the US average of 78.6%. That gap is worth roughly 55 fewer late arrivals for every thousand flights.
Key figures
On time
84.1%
Arrivals under 15 minutes late, of 5,428 completed departures
Avg delay
78 min
Across delayed arrivals only, not all flights
Cancelled
0.57%
Nationally in May: 0.92%
Whole year
81.1%
IAD across all twelve months
These figures cover 5,474 departures from Washington Dulles 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 IAD's other months
Against IAD's own year, May ran 3 points better than the twelve-month rate of 81.1%, which makes it number four of twelve months, best first. Cancellations were unusually low for IAD in May, at 0.57% against 1.37% across the year. Either side of it, April ran 87.2% on time and June 78.1%, so this month sits in line with its neighbours.
| 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 | 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 (this page) | 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 May
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 17 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am491 flights88.5%
- 8am–11am1,322 flights92.3%
- 11am–2pm1,045 flights86.3%
- 2pm–5pm323 flights83.8%
- 5pm–8pm1,423 flights75.2%
- 8pm–5am870 flights81.0%
Scale runs 65% to 100%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 92.3% of the time, against 75.2% for the evening window. That is 17 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 1,423 flights scheduled in it.
Across the week, Saturday is the strongest day at 88.2% on time and Wednesday the weakest at 69.4%. 19 points is a smaller lever than departure hour, but it is free.
Carrier by carrier
Which airlines ran best at IAD in May
The two carriers here are closely matched: half a point 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.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 3,541 | 85.1% | 65 min | 0.23% | A+ |
| Republic Airways | 718 | 85.1% | 85 min | 1.53% | A |
| Delta Air Linesthin sample | 299 | 84.2% | 76 min | 2.34% | B |
| SkyWest Airlinesthin sample | 259 | 84.7% | 191 min | 0.39% | B+ |
| Frontier Airlinesthin sample | 167 | 73.1% | 92 min | 0.00% | C+ |
| American Airlinesthin sample | 162 | 73.4% | 85 min | 1.85% | C |
| Alaska Airlinesthin sample | 120 | 84.2% | 53 min | 0.00% | B+ |
| Southwest Airlinesthin sample | 93 | 71.7% | 35 min | 0.00% | C+ |
| PSA Airlinesthin sample | 67 | 84.8% | 282 min | 1.49% | B |
| Allegiant Airthin sample | 48 | 83.3% | 175 min | 0.00% | B+ |
No carrier stands out. United tops the table at 85.1%, half a point 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 May
| Route | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| IAD to ATL · Atlanta | 405 | 75.6% | 64 min | 1.48% | B |
| IAD to DEN · Denverthin sample | 316 | 85.0% | 54 min | 0.00% | A+ |
| IAD to SFO · San Franciscothin sample | 268 | 79.8% | 62 min | 0.00% | B+ |
| IAD to LAX · Los Angelesthin sample | 252 | 87.6% | 45 min | 0.40% | A+ |
| IAD to ORD · Chicagothin sample | 217 | 76.9% | 65 min | 0.00% | B+ |
| IAD to SEA · Seattlethin sample | 201 | 86.1% | 58 min | 0.00% | A+ |
| IAD to MCO · Orlandothin sample | 197 | 85.8% | 72 min | 0.00% | A+ |
| IAD to DFW · Dallas-Fort Worththin sample | 175 | 74.6% | 142 min | 1.71% | C |
| IAD to CLT · Charlottethin sample | 174 | 86.6% | 149 min | 0.57% | A+ |
| IAD to IAH · Houstonthin sample | 167 | 83.1% | 58 min | 0.60% | B+ |
| IAD to DTW · Detroitthin sample | 144 | 87.3% | 103 min | 1.39% | A |
| IAD to EWR · Newarkthin sample | 135 | 89.4% | 66 min | 2.22% | A |
| IAD to BOS · Bostonthin sample | 124 | 81.3% | 69 min | 0.81% | B+ |
| IAD to SAN · San Diegothin sample | 120 | 84.2% | 55 min | 0.00% | B+ |
| IAD to PWM · Portlandthin sample | 114 | 92.9% | 158 min | 0.88% | A+ |
| IAD to RDU · Raleighthin sample | 112 | 90.2% | 119 min | 0.00% | A+ |
| IAD to CLE · Clevelandthin sample | 104 | 89.3% | 77 min | 0.96% | A+ |
| IAD to MSP · Minneapolisthin sample | 101 | 86.1% | 144 min | 0.00% | A+ |
| IAD to TPA · Tampathin sample | 97 | 90.7% | 70 min | 0.00% | A+ |
| IAD to PHX · Phoenixthin sample | 96 | 84.4% | 59 min | 0.00% | B+ |
| IAD to LGA · New Yorkthin sample | 96 | 75.3% | 39 min | 3.12% | B− |
| IAD to BDL · Hartfordthin sample | 95 | 83.2% | 83 min | 0.00% | B+ |
| IAD to IND · Indianapolisthin sample | 92 | 90.1% | 49 min | 1.09% | A |
| IAD to AUS · Austinthin sample | 88 | 84.1% | 37 min | 0.00% | B+ |
| IAD to PIT · Pittsburghthin sample | 88 | 87.4% | 100 min | 1.14% | A |
Delay causes
What held IAD up in May
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.
- 36%Late-arriving aircraft
- 32%Carrier
- 25%National Airspace System
- 7%Extreme weather
- 0%Security
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 68,000 reported delay minutes here, that single category outweighs weather by 5 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 67,554 reported delay minutes.
Cancellations are rare at 0.57%, 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.
5.2% of arrivals land an hour or more late, close to the national 7.1%. 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 May
For a May trip through IAD: expect 84.1% on time and 0.57% cancelled, going by May 2026. The 8am–11am window was the strongest part of the day.
Related
Where to go next
- Washington Dulles International (IAD), the whole year
- IAD in July69.5%
- IAD in August81.0%
- 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 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.