Route reliability record

IAH→DCA

Houston to Washington

Flights: 3,202
Period: July 2025 to June 2026
Distance: 1,208 mi
Carriers: 3

This route sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.6%. The late ones land a little over an hour behind schedule. That rests on 3,202 flights, of which Republic Airways flew 513 at 75.9% on time.

The US average over the same twelve months is 77.6%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.

On time

74.8%

Arrivals under 15 minutes late, of 3,130 completed flights

Avg delay

73 min

Across delayed arrivals only, not all flights

Cancelled

1.81%

National rate is 1.81%

Best carrier

Republic

75.9% on time across 513 flights

These figures cover 3,202 flights between July 2025 and June 2026. Beyond the headline rate, 9.5% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.

Carrier by carrier

Which airline is most reliable on IAH to DCA

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.

On-time performance by carrier on IAH to DCA
Airline	Flights	On time	Avg delay	Cancelled	Grade
Republic Airways	513	75.9%	64 min	4.87%	B−
United Airlines	2,413	75.2%	70 min	0.79%	B+
PSA Airlinesthin sample	276	69.0%	109 min	5.07%	C−

Republic Airways cancels 4.9% of what it schedules here, the highest in the table. A cancelled flight never appears in an on-time rate, so read that column alongside the punctuality one rather than after it.

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 26 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–8am648 flights90.2%
8am–11am543 flights79.4%
11am–2pm381 flights76.6%
2pm–5pm531 flights69.1%
5pm–8pm757 flights64.0%
8pm–5am342 flights68.9%

Scale runs 55% to 95%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 64.0% on time, against 90.2% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 5pm–8pm window is the busiest, with 757 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 25 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.

Darker means more delays. Figures are on-time percentages.January best, July worst

July is the worst month at 58.6% on time, 25 points below January, the best at 84.0%. 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. October was the busiest month here, with 291 flights.

Across the week, Tuesday is the strongest day at 80.3% on time and Friday the weakest at 71.6%. 9 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 57,000 reported delay minutes.

National Airspace System
36%
Late-arriving aircraft
34%
Carrier
19%
Extreme weather
11%
Security
0%

Extreme weather accounts for 11% of delay minutes, well above the single-digit share typical across the system. Weather delays are lumpy: they arrive as whole bad days rather than as a steady drag, so the monthly strip above is the more useful view of the risk. The national share is 6%, so this operation carries roughly 1.8 times the usual weather exposure. The split is drawn from 57,463 reported delay minutes.

36% 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 21,000 minutes out of 57,000, against a national NAS share of 21%.

Cancellations sit at 1.81% against a national 1.81%, which is ordinary. Diversions add another 0.44%.

Connections and stage length

What a delay here actually costs

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 9.5% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.

The 1,208 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 81.4% on time across 3,200 flights, 7 points above 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 7 points of difference.

The sample behind these figures is 3,202 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.

What to do with this

Booking this route

Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 84.0% on time and July 58.6%, a swing of 25 points. If the dates move at all, move them out of July before you think about anything else. 3,130 completed flights over 12 months sit behind that.

Common questions

IAH to DCA questions

How often is IAH to DCA delayed?

About one flight in four arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 25.2% of the 3,202 flights in this analysis, against 22.4% nationally. Delayed flights are late by a little over an hour on average.

Which airline is most reliable on IAH to DCA?

Republic Airways leads at 75.9% on time across 513 flights. United Airlines is at the other end on 75.2%, a gap of half a point. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.

What time of day has the fewest delays on IAH to DCA?

The 5am–8am departure window is the strongest at 90.2% on time. The 5pm–8pm window is the weakest at 64.0%, 26 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 DCA?

July is the weakest month at 58.6% on time, compared with 84.0% in January. Across the year that is 25 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.

Where to go next

Direction matters. IAH to DCA and DCA to IAH are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.

Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Updated monthly. How this data is collected.

Key figures