Route reliability record

DCA→IAH

Washington to Houston

Flights: 3,200
Period: July 2025 to June 2026
Distance: 1,208 mi
Carriers: 3

This route lands a B, 4 points better than the national rate of 77.6%. About one flight in five arrive 15 minutes late or worse, and those flights are late by an hour and a half on average. That is a workable record, not a spotless one. That rests on 3,200 flights, of which United Airlines flew 2,413 at 83.8% 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

81.4%

Arrivals under 15 minutes late, of 3,125 completed flights

Avg delay

84 min

Across delayed arrivals only, not all flights

Cancelled

1.97%

National rate is 1.81%

Best carrier

United

83.8% on time across 2,413 flights

These figures cover 3,200 flights between July 2025 and June 2026. Beyond the headline rate, 8.0% 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 DCA to IAH

The choice of carrier is not cosmetic here. United Airlines arrives on time 83.8% of the time; Republic Airways manages 75.7%. Sample sizes sit next to every figure, because a two-point gap across 511 flights means less than a ten-point one.

On-time performance by carrier on DCA to IAH
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	2,413	83.8%	95 min	0.91%	B+
Republic Airways	511	75.7%	56 min	5.09%	B−
PSA Airlinesthin sample	276	70.1%	73 min	5.43%	C−

Republic Airways cancels 5.1% 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 38 points, against 8 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am584 flights89.8%
8am–11am371 flights92.0%
11am–2pm776 flights87.3%
2pm–5pm810 flights72.3%
5pm–8pm123 flights54.2%
8pm–5am536 flights76.4%

Scale runs 45% to 95%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 54.2% on time, against 92.0% for the 8am–11am 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 2pm–5pm window is the busiest, with 810 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 19 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.February best, May worst

Delays peak in May, when the on-time rate falls to 70.9%. February is the strongest month at 89.7%. Moving a flexible trip across that boundary buys 19 points. October was the busiest month here, with 291 flights.

Across the week, Saturday is the strongest day at 85.7% on time and Friday the weakest at 77.0%. 9 points is a smaller lever than departure hour, but it is free.

Delay causes

Why this route gets delayed

One category carries most of the weight here. Late-arriving aircraft accounts for 43% of the 49,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.

Late-arriving aircraft
43%
National Airspace System
27%
Carrier
24%
Extreme weather
5%
Security
0%

43% 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 49,000 reported delay minutes here, that single category outweighs weather by 8 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 48,823 reported delay minutes.

The practical consequence: the 8am–11am 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.

Cancellations sit at 1.97% against a national 1.81%, which is ordinary. Diversions add another 0.38%.

Connections and stage length

What a delay here actually costs

8.0% 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 are the an hour and a half kind, which a normal layover absorbs.

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 74.8% on time across 3,202 flights, 7 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 7 points of difference.

The sample behind these figures is 3,200 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. February runs 89.7% on time and May 70.9%, a swing of 19 points. If the dates move at all, move them out of May before you think about anything else. 3,125 completed flights over 12 months sit behind that.

Common questions

DCA to IAH questions

How often is DCA to IAH delayed?

About one flight in five arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 18.6% of the 3,200 flights in this analysis, against 22.4% nationally. Delayed flights are late by an hour and a half on average.

Which airline is most reliable on DCA to IAH?

United Airlines leads at 83.8% on time across 2,413 flights. Republic Airways is at the other end on 75.7%, a gap of 8 points. 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 DCA to IAH?

The 8am–11am departure window is the strongest at 92.0% on time. The 5pm–8pm window is the weakest at 54.2%, 38 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 May delays on DCA to IAH?

May is the weakest month at 70.9% on time, compared with 89.7% in February. Across the year that is 19 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. DCA to IAH and IAH to DCA 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