Route reliability record
DEN→IAH
Denver to Houston
- Flights
- 4,728
- Period
- September 2025 to August 2026
- Distance
- 861 mi
- Carriers
- 2
This route lands a B+, 2 points better than the national rate of 77.3%. About one flight in five arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 4,728 DEN to IAH flights, of which United Airlines flew 3,894 at 79.7% on time.
Best time to fly DEN to IAH: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 91.9% of the time and Tuesday flights 85.0%, against 79.6% for the route overall.
The US average over the same twelve months is 77.3%, 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.
Key figures
On time
79.6%
Arrivals under 15 minutes late, of 4,707 completed flights
Avg delay
62 min
Across delayed arrivals only, not all flights
Cancelled
0.30%
National rate is 1.89%
Best carrier
United
79.7% on time across 3,894 flights
These figures cover 4,728 flights between September 2025 and August 2026. The median arrival is 7 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 DEN to IAH
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.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 3,894 | 79.7% | 63 min | 0.26% | B+ |
| Frontier Airlines | 834 | 79.3% | 58 min | 0.48% | B+ |
No carrier stands out. United tops the table at 79.7%, half a point clear of the bottom, which is inside the range this kind of sample moves year to year.
Flight by flight
Flights on DEN 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 Denver 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. 1 of the top 3 use a different airport at one end.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. DEN → IAHDenver to Houston | United Airlines | 79.5% | 79.7% | 0.26% | 5am–8am, Tue | UA 320 05:00 |
| 2. DEN → IAHDenver to Houston | Frontier Airlines | 78.9% | 79.3% | 0.48% | 11am–2pm, Sat | F9 3206 07:00 |
| 3. DEN → HOUDenver to Houston | Southwest Airlines | 74.6% | 75.0% | 0.56% | 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 18 points, against half a point between the best and worst carrier.
- 5am–8am1,003 flights91.9%
- 8am–11am396 flights82.7%
- 11am–2pm772 flights76.6%
- 2pm–5pm682 flights78.0%
- 5pm–8pm1,108 flights73.6%
- 8pm–5am767 flights75.2%
Scale runs 65% to 95%.
Book the early departure. Flights leaving between 5am–8am arrive on time 91.9% of the time, against 73.6% for the evening window. That is 18 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 5pm–8pm window is the busiest, with 1,108 flights scheduled in it.
Explore
Filter DEN 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 DEN to IAH, the best departure window is 5am–8am at 91.9% on time and the worst is 5pm–8pm at 73.6%, a wide gap of 18.3 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am91.9%
- 8–11am82.7%
- 11am–2pm76.6%
- 2–5pm78.0%
- 5–8pm73.6%
- 8pm–5am75.2%
best all US flightsScale 60% to 95%.
Across the year
When delays peak on this route
This route's year swings by 18 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.
June is the worst month at 68.6% on time, 18 points below January, the best at 86.9%. 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. July was the busiest month here, with 444 flights.
Across the week, Tuesday is the strongest day at 85.0% on time and Friday the weakest at 76.8%, a spread of 8 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 59,000 reported delay minutes.
- 42%Late-arriving aircraft
- 29%Carrier
- 28%National Airspace System
- 1%Extreme weather
42% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 59,000 reported delay minutes here, that single category outweighs weather by 31 to one. The split is drawn from 59,183 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 91.9% on time here.
Cancellations are rare at 0.30%, 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
6.9% 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 861 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 is a different operation and performs like one: it runs 83.0% on time across 4,728 flights, 3 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 3 points of difference.
The sample behind these figures is 4,728 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. January runs 86.9% on time and June 68.6%, a swing of 18 points. If the dates move at all, move them out of June before you think about anything else. 4,707 completed flights over 12 months sit behind that.
Common questions
DEN to IAH questions
How often is DEN to IAH delayed?
About one flight in five arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 20.4% of the 4,728 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on DEN to IAH?
United Airlines leads at 79.7% on time across 3,894 flights. Frontier Airlines is at the other end on 79.3%, 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 DEN to IAH?
The 5am–8am departure window is the strongest at 91.9% on time. The 5pm–8pm window is the weakest at 73.6%, 18 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 June delays on DEN to IAH?
June is the weakest month at 68.6% on time, compared with 86.9% in January. Across the year that is 18 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 DEN — the return legseparate record
- Denver International (DEN) delay statistics
- George Bush Intercontinental (IAH) delay statistics
- United Airlines on DEN to IAH79.7%
- Frontier Airlines on DEN to IAH79.3%
- DEN to PHX, a related route75.6%
- ORD to IAH, a related route76.0%
- DEN to SLC, a related route78.2%
- United Airlines on-time record79.7%
- Frontier Airlines on-time record79.3%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 million flight records
Direction matters. DEN to IAH and IAH to DEN 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.