Route reliability record
IAH→SFO
Houston to San Francisco
- Flights
- 3,600
- Period
- July 2025 to June 2026
- Distance
- 1,635 mi
- Carriers
- 1
This route lands a B+, about a point 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 about an hour on average. That is a workable record, not a spotless one. That rests on 3,600 flights, with a median arrival 7 minutes early.
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.
Key figures
On time
78.6%
Arrivals under 15 minutes late, of 3,581 completed flights
Avg delay
66 min
Across delayed arrivals only, not all flights
Cancelled
0.47%
National rate is 1.81%
Best carrier
United
78.6% 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 IAH to SFO
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 | 78.6% | 66 min | 0.47% | 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 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–8am730 flights92.8%
- 8am–11am459 flights74.7%
- 11am–2pm366 flights80.1%
- 2pm–5pm828 flights79.2%
- 5pm–8pm508 flights66.7%
- 8pm–5am709 flights73.6%
Scale runs 60% to 100%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 92.8% of the time, against 66.7% for the evening window. That is 26 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 2pm–5pm window is the busiest, with 828 flights scheduled in it.
Across the year
When delays peak on this route
This route's year swings by 32 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 57.2% on time, 32 points below September, the best at 89.3%. 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. December was the busiest month here, with 311 flights.
Across the week, Tuesday is the strongest day at 86.9% on time and Monday the weakest at 72.6%. 14 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 50,000 reported delay minutes.
- 42%National Airspace System
- 28%Late-arriving aircraft
- 26%Carrier
- 5%Extreme weather
42% 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 50,000, against a national NAS share of 21%. The split is drawn from 50,352 reported delay minutes.
Cancellations are rare at 0.47%, 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
7.6% 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 about an hour kind, which a normal layover absorbs.
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 84.8% on time across 3,600 flights, 6 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 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 89.3% on time and June 57.2%, a swing of 32 points. If the dates move at all, move them out of June before you think about anything else. 3,581 completed flights over 12 months sit behind that.
Common questions
IAH to SFO questions
How often is IAH to SFO 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 21.4% of the 3,600 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.
How reliable is IAH to SFO compared with the rest of the country?
78.6% of flights arrive on time here against a national 77.6%, a difference of about a point in its favour. That is worth a B+ on this site's grading scale.
What time of day has the fewest delays on IAH to SFO?
The 5am–8am departure window is the strongest at 92.8% on time. The 5pm–8pm window is the weakest at 66.7%, 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 June delays on IAH to SFO?
June is the weakest month at 57.2% on time, compared with 89.3% in September. Across the year that is 32 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
- SFO to IAH — the return legseparate record
- George Bush Intercontinental (IAH) delay statistics
- San Francisco International (SFO) delay statistics
- United Airlines on-time record78.6%
- 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. IAH to SFO and SFO 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.