Route reliability record
IAH→IAD
Houston to Washington
- Flights
- 1,860
- Period
- September 2025 to August 2026
- Distance
- 1,190 mi
- Carriers
- 1
This route lands a B+, 5 points better than the national rate of 77.3%. About one flight in six arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 1,860 IAH to IAD flights, with a median arrival 5 minutes early.
Best time to fly IAH to IAD: a 5am–8am departure, ideally on a Monday. Flights in that window arrived on time 92.0% of the time and Monday flights 85.8%, against 82.4% for the route overall.
Set against the rest of the country, this route's record is 5 points better than the US average of 77.3%. That gap is worth roughly 51 fewer late arrivals for every thousand flights.
Key figures
On time
82.4%
Arrivals under 15 minutes late, of 1,849 completed flights
Avg delay
62 min
Across delayed arrivals only, not all flights
Cancelled
0.43%
National rate is 1.89%
Best carrier
United
82.4% on time across 1,860 flights
These figures cover 1,860 flights between September 2025 and August 2026. The median arrival is 5 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.
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Carrier by carrier
Which airline is most reliable on IAH to IAD
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.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 1,860 | 82.4% | 62 min | 0.43% | B+ |
Flight by flight
Flights on IAH to IAD
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
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Best ways to make this trip
The most reliable ways to fly Houston to Washington
Every airline on this route and on the routes between nearby airports, ranked by how often a scheduled flight actually operated and arrived on time. 4 of the top 5 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. IAH → IADHouston to Washington | United Airlines | 82.0% | 82.4% | 0.43% | 5am–8am, Mon | UA 1549 07:20 |
| 2. IAH → BWIHouston to Baltimore | United Airlines | 80.8% | 81.3% | 0.60% | 5am–8am, Tue | — |
| 3. IAH → DCAHouston to Washington | United Airlines | 76.2% | 76.7% | 0.67% | 5am–8am, Tue | UA 654 12:00 |
| 4. HOU → BWIHouston to Baltimore | Southwest Airlines | 73.9% | 74.9% | 1.35% | 5am–8am, Wed | — |
| 5. IAH → DCAHouston to Washington | Republic Airways | 72.2% | 75.9% | 4.87% | 5am–8am, Sat | — |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
Departure window
The best time of day to leave
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 14 points, against half a point between the best and worst carrier.
- 5am–8am364 flights92.0%
- 8am–11am1 flights—
- 11am–2pm388 flights82.9%
- 2pm–5pm428 flights79.3%
- 5pm–8pm400 flights79.6%
- 8pm–5am279 flights77.8%
Scale runs 70% to 95%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 92.0% of the time, against 77.8% for the overnight window. That is 14 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 2pm–5pm window is the busiest, with 428 flights scheduled in it.
Explore
Filter IAH to IAD by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On IAH to IAD, the best departure window is 5am–8am at 92.0% on time and the worst is 8pm–5am at 77.8%, a wide gap of 14.2 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am92.0%
- 8–11am—
- 11am–2pm82.9%
- 2–5pm79.3%
- 5–8pm79.6%
- 8pm–5am77.8%
best all US flightsScale 60% to 95%. Cells under 30 flights show a dash.
Across the year
When delays peak on this route
This route's year swings by 23 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.
July is the worst month at 69.8% on time, 23 points below September, the best at 92.7%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. September was the busiest month here, with 193 flights.
Across the week, Monday is the strongest day at 85.8% on time and Friday the weakest at 79.9%, a spread of 6 points.
Delay causes
Why this route gets delayed
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 20,000 reported delay minutes.
- 32%National Airspace System
- 31%Carrier
- 31%Late-arriving aircraft
- 6%Extreme weather
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 92.0% on time here. The split is drawn from 20,167 reported delay minutes.
No single cause dominates. national airspace system at 32%, carrier at 31% and late-arriving aircraft at 31% split the 20,000 reported delay minutes between them. An even spread like this usually means the operation is running close to its designed capacity with no one obvious weak point, and it is the hardest pattern for a traveller to route around.
Cancellations are rare at 0.43%, below the national 1.89% 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.
Connections and stage length
What a delay here actually costs
5.8% of arrivals land an hour or more late, close to the national 8.3%, so a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last about an hour, which a normal layover absorbs.
The 1,190 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty.
The return leg runs 84.7% on time across 1,862 flights, within 2 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.
The sample behind these figures is 1,860 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.
Work out the risk of missing a connection in IAD after this flight
What to do with this
Booking this route
Put together: the calendar is the biggest lever here, not the carrier or the hour. September runs 92.7% on time and July 69.8%, a swing of 23 points. If the dates move at all, move them out of July before you think about anything else. 1,849 completed flights over 12 months sit behind that.
Common questions
IAH to IAD questions
How often is IAH to IAD delayed?
About one flight in six arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 17.6% of the 1,860 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
How reliable is IAH to IAD compared with the rest of the country?
82.4% of flights arrive on time here against a national 77.3%, a difference of 5 points in its favour. That is worth a B+ on this site's grading scale.
What time of day has the fewest delays on IAH to IAD?
The 5am–8am departure window is the strongest at 92.0% on time. The 8pm–5am window is the weakest at 77.8%, 14 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.
How bad are July delays on IAH to IAD?
July is the weakest month at 69.8% on time, compared with 92.7% in September. Across the year that is 23 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- IAD to IAH — the return legseparate record
- George Bush Intercontinental (IAH) delay statistics
- Washington Dulles International (IAD) delay statistics
- IAH to ORD, a related route75.1%
- ATL to IAD, a related route76.4%
- IAH to DFW, a related route76.4%
- United Airlines on-time record82.4%
- The best time of day to fly, according to 7.05 million flight records
- Worst months to fly in the US, ranked by the data
Direction matters. IAH to IAD and IAD to IAH are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.
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Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.