Route reliability record
IAD→IAH
Washington to Houston
- Flights
- 1,869
- Period
- July 2025 to June 2026
- Distance
- 1,190 mi
- Carriers
- 1
This route lands a B+, 6 points better than the national rate of 77.6%. About one flight in six 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 1,869 IAD to IAH flights, with a median arrival 10 minutes early.
Best time to fly IAD to IAH: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 90.8% of the time and Tuesday flights 87.9%, against 83.7% for the route overall.
Set against the rest of the country, this route's record is 6 points better than the US average of 77.6%. That gap is worth roughly 61 fewer late arrivals for every thousand flights.
Key figures
On time
83.7%
Arrivals under 15 minutes late, of 1,857 completed flights
Avg delay
68 min
Across delayed arrivals only, not all flights
Cancelled
0.48%
National rate is 1.81%
Best carrier
United
83.7% on time across 1,869 flights
These figures cover 1,869 flights between July 2025 and June 2026. The median arrival is 10 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.
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 | 1,869 | 83.7% | 68 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.
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 | 83.3% | 83.7% | 0.48% | 5am–8am, Tue | UA 1524 08:30 |
| 2. DCA → IAHWashington to Houston | United Airlines | 83.0% | 83.8% | 0.91% | 5am–8am, Tue | UA 1450 06:00 |
| 3. BWI → IAHBaltimore to Houston | United Airlines | 82.3% | 83.2% | 1.10% | 5am–8am, Tue | — |
| 4. DCA → HOUWashington to Houston | Southwest Airlines | 76.1% | 77.5% | 1.80% | 5am–8am, Mon | — |
| 5. BWI → HOUBaltimore to Houston | Southwest Airlines | 75.1% | 76.3% | 1.58% | 5am–8am, Tue | — |
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. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am347 flights90.8%
- 8am–11am396 flights89.1%
- 11am–2pm398 flights85.3%
- 2pm–5pm76 flights77.3%
- 5pm–8pm366 flights70.7%
- 8pm–5am286 flights83.7%
Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 90.8% of the time, against 70.7% 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 11am–2pm window is the busiest, with 398 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 22 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 72.1% on time, 22 points below February, the best at 93.8%. 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 195 flights.
Across the week, Tuesday is the strongest day at 87.9% on time and Friday the weakest at 81.5%. 6 points is a smaller lever than departure hour, but it is free.
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 21,000 reported delay minutes.
- 35%National Airspace System
- 30%Late-arriving aircraft
- 29%Carrier
- 6%Extreme weather
35% 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 7,186 minutes out of 21,000, against a national NAS share of 21%. The split is drawn from 20,739 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 90.8% on time here.
Cancellations are rare at 0.48%, below the national 1.81% 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
5.7% of arrivals land an hour or more late, close to the national 8.1%. 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.
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. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.
The return leg is a different operation and performs like one: it runs 80.4% on time across 1,867 flights, 3 points below this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 3 points of difference.
The sample behind these figures is 1,869 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 July 72.1%, a swing of 22 points. If the dates move at all, move them out of July before you think about anything else. 1,857 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 six arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 16.3% of the 1,869 flights in this analysis, against 22.4% 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?
83.7% of flights arrive on time here against a national 77.6%, a difference of 6 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 90.8% on time. The 5pm–8pm window is the weakest at 70.7%, 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 July delays on IAD to IAH?
July is the weakest month at 72.1% on time, compared with 93.8% in February. Across the year that is 22 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 route79.2%
- ORD to IAH, a related route75.0%
- IAD to DEN, a related route81.7%
- United Airlines on-time record83.7%
- The best time of day to fly, according to 7.04 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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.