Route reliability record
SFO→IAH
San Francisco to Houston
- Flights
- 3,600
- Period
- July 2025 to June 2026
- Distance
- 1,635 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 77.6%. When something does go wrong the average delay runs roughly 55 minutes. That rests on 3,600 flights, with a median arrival 7 minutes early.
Set against the rest of the country, this route's record is 7 points better than the US average of 77.6%. That gap is worth roughly 72 fewer late arrivals for every thousand flights.
Key figures
On time
84.8%
Arrivals under 15 minutes late, of 3,579 completed flights
Avg delay
53 min
Across delayed arrivals only, not all flights
Cancelled
0.28%
National rate is 1.81%
Best carrier
United
84.8% on time across 3,600 flights
These figures cover 3,600 flights between July 2025 and June 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.
Carrier by carrier
Which airline is most reliable on SFO 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 | 3,600 | 84.8% | 53 min | 0.28% | B+ |
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 21 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–8am726 flights96.1%
- 8am–11am513 flights79.1%
- 11am–2pm582 flights75.5%
- 2pm–5pm705 flights83.0%
- 5pm–8pm345 flights86.1%
- 8pm–5am729 flights85.9%
Scale runs 65% to 100%. Rows with fewer than 30 flights show a dash.
The weak window here is the middle of the day, not the evening: 11am–2pm runs 75.5% on time against 96.1% for 5am–8am. That shape usually means a departure bank rather than an accumulating delay, so the recovery later in the afternoon is real rather than noise. The 8pm–5am window is the busiest, with 729 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 14 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.
September is the best month on the calendar at 92.4% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. December was the busiest month here, with 311 flights.
Across the week, Tuesday is the strongest day at 86.6% on time and Monday the weakest at 82.2%. 4 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 29,000 reported delay minutes.
- 39%Carrier
- 31%Late-arriving aircraft
- 29%National Airspace System
- 1%Extreme weather
The largest share of delay minutes, 39%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 11,000 of the 29,000 delay minutes reported here. The split is drawn from 28,722 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 96.1% on time here.
Cancellations are rare at 0.28%, 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
Badly late arrivals are rare here: only 3.8% land an hour or more behind schedule, against 8.1% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
At 1,635 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.
The return leg is a different operation and performs like one: it runs 78.6% on time across 3,600 flights, 6 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 6 points of difference.
The sample behind these figures is 3,600 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. September runs 92.4% on time and May 78.8%, a swing of 14 points. If the dates move at all, move them out of May before you think about anything else. 3,579 completed flights over 12 months sit behind that.
Common questions
SFO to IAH questions
How often is SFO to IAH delayed?
About one flight in seven arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 15.2% of the 3,600 flights in this analysis, against 22.4% nationally. Delayed flights are late by roughly 55 minutes on average.
How reliable is SFO to IAH compared with the rest of the country?
84.8% of flights arrive on time here against a national 77.6%, 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 SFO to IAH?
The 5am–8am departure window is the strongest at 96.1% on time. The 11am–2pm window is the weakest at 75.5%, 21 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 SFO to IAH?
May is the weakest month at 78.8% on time, compared with 92.4% in September. Across the year that is 14 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 SFO — the return legseparate record
- San Francisco International (SFO) delay statistics
- George Bush Intercontinental (IAH) delay statistics
- United Airlines on-time record84.8%
- 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. SFO to IAH and IAH to SFO 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.