Route reliability record
IAD→IAH
Washington to Houston
- Flights
- 1,862
- Period
- September 2025 to August 2026
- Distance
- 1,190 mi
- Carriers
- 1
This route 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 7 points better than the national rate of 77.3%. When something does go wrong the average delay runs a little over an hour. That rests on 1,862 IAD to IAH flights, with a median arrival 11 minutes early.
Best time to fly IAD to IAH: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 91.6% of the time and Tuesday flights 87.4%, against 84.7% for the route overall.
Set against the rest of the country, this route's record is 7 points better than the US average of 77.3%. That gap is worth roughly 74 fewer late arrivals for every thousand flights.
Key figures
On time
84.7%
Arrivals under 15 minutes late, of 1,849 completed flights
Avg delay
71 min
Across delayed arrivals only, not all flights
Cancelled
0.48%
National rate is 1.89%
Best carrier
United
84.7% on time across 1,862 flights
These figures cover 1,862 flights between September 2025 and August 2026. The median arrival is 11 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 IAD to IAH
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 | 1,862 | 84.7% | 71 min | 0.48% | B+ |
Flight by flight
Flights on IAD to IAH
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 Washington to Houston
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. IAD → IAHWashington to Houston | United Airlines | 84.3% | 84.7% | 0.48% | 5am–8am, Tue | UA 1524 08:30 |
| 2. BWI → IAHBaltimore to Houston | United Airlines | 83.0% | 84.0% | 1.20% | 5am–8am, Thu | — |
| 3. DCA → IAHWashington to Houston | United Airlines | 82.8% | 83.5% | 0.80% | 5am–8am, Wed | UA 1450 06:00 |
| 4. BWI → HOUBaltimore to Houston | Southwest Airlines | 74.6% | 75.7% | 1.43% | 5am–8am, Wed | — |
| 5. DCA → HOUWashington to Houston | Southwest Airlines | 73.8% | 75.4% | 2.18% | 5am–8am, Wed | — |
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 20 points, against half a point between the best and worst carrier.
- 5am–8am345 flights91.6%
- 8am–11am396 flights89.3%
- 11am–2pm386 flights87.4%
- 2pm–5pm83 flights76.5%
- 5pm–8pm366 flights72.0%
- 8pm–5am286 flights85.2%
Scale runs 65% to 95%.
Book the early departure. Flights leaving between 5am–8am arrive on time 91.6% of the time, against 72.0% for the evening window. That is 20 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 396 flights scheduled in it.
Explore
Filter IAD to IAH 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 IAD to IAH, the best departure window is 5am–8am at 91.6% on time and the worst is 5pm–8pm at 72.0%, a wide gap of 19.6 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am91.6%
- 8–11am89.3%
- 11am–2pm87.4%
- 2–5pm76.5%
- 5–8pm72.0%
- 8pm–5am85.2%
best all US flightsScale 60% to 95%.
Across the year
When delays peak on this route
This route's year swings by 16 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.
December is the weak month at 77.7% on time, against 93.8% in February. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. September was the busiest month here, with 195 flights.
Across the week, Tuesday is the strongest day at 87.4% on time and Saturday the weakest at 81.5%, 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
- 32%Late-arriving aircraft
- 29%Carrier
- 7%Extreme weather
32% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 6,432 minutes out of 20,000, against a national NAS share of 21%. The split is drawn from 20,081 reported delay minutes.
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 91.6% on time here.
Cancellations are rare at 0.48%, 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
5.4% 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 a little over 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 82.4% on time across 1,860 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 1,862 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 IAH 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. February runs 93.8% on time and December 77.7%, a swing of 16 points. If the dates move at all, move them out of December before you think about anything else. 1,849 completed flights over 12 months sit behind that.
Common questions
IAD to IAH questions
How often is IAD to IAH delayed?
About one flight in seven arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 15.3% of the 1,862 flights in this analysis, against 22.7% nationally. Delayed flights are late by a little over an hour on average.
How reliable is IAD to IAH compared with the rest of the country?
84.7% of flights arrive on time here against a national 77.3%, a difference of 7 points in its favour. That is worth a B+ on this site's grading scale.
What time of day has the fewest delays on IAD to IAH?
The 5am–8am departure window is the strongest at 91.6% on time. The 5pm–8pm window is the weakest at 72.0%, 20 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 December delays on IAD to IAH?
December is the weakest month at 77.7% on time, compared with 93.8% in February. Across the year that is 16 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
- IAH to IAD — the return legseparate record
- Washington Dulles International (IAD) delay statistics
- George Bush Intercontinental (IAH) delay statistics
- IAD to ATL, a related route78.0%
- ORD to IAH, a related route76.0%
- IAD to DEN, a related route83.1%
- United Airlines on-time record84.7%
- 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. IAD to IAH and IAH to IAD 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.