Route reliability record
IAH→SFO
Houston to San Francisco
- Flights
- 3,578
- Period
- September 2025 to August 2026
- Distance
- 1,635 mi
- Carriers
- 1
This route lands a B+, about a point better than the national rate of 77.3%. Roughly one flight in five arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 3,578 IAH to SFO flights, with a median arrival 7 minutes early.
Best time to fly IAH to SFO: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 92.9% of the time and Tuesday flights 85.4%, against 78.2% 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
78.2%
Arrivals under 15 minutes late, of 3,560 completed flights
Avg delay
62 min
Across delayed arrivals only, not all flights
Cancelled
0.42%
National rate is 1.89%
Best carrier
United
78.2% on time across 3,578 flights
These figures cover 3,578 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 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 | 3,578 | 78.2% | 62 min | 0.42% | B+ |
Flight by flight
Flights on IAH to SFO
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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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 29 points, against half a point between the best and worst carrier.
- 5am–8am709 flights92.9%
- 8am–11am521 flights72.1%
- 11am–2pm366 flights77.9%
- 2pm–5pm869 flights80.2%
- 5pm–8pm496 flights64.0%
- 8pm–5am617 flights75.2%
Scale runs 55% to 100%.
The 5pm–8pm window is where this operation falls apart: 64.0% on time, against 92.9% 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 2pm–5pm window is the busiest, with 869 flights scheduled in it.
Explore
Filter IAH to SFO 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 IAH to SFO, the best departure window is 5am–8am at 92.9% on time and the worst is 5pm–8pm at 64.0%, a wide gap of 28.9 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am92.9%
- 8–11am72.1%
- 11am–2pm77.9%
- 2–5pm80.2%
- 5–8pm64.0%
- 8pm–5am75.2%
best all US flightsScale 55% to 95%.
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 85.4% on time and Monday the weakest at 70.6%, a spread of 15 points.
Delay causes
Why this route gets delayed
National Airspace System accounts for 49% of the 48,000 delay minutes carriers reported here, and the remaining four split what is left.
- 49%National Airspace System
- 25%Late-arriving aircraft
- 23%Carrier
- 3%Extreme weather
49% 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 24,000 minutes out of 48,000, against a national NAS share of 21%. The split is drawn from 47,987 reported delay minutes.
Cancellations are rare at 0.42%, 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
7.0% 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.
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 84.0% on time across 3,578 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 3,578 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 SFO 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. 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. 3,560 completed flights over 12 months sit behind that.
Common questions
IAH to SFO questions
How often is IAH to SFO delayed?
Roughly 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 21.8% of the 3,578 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
How reliable is IAH to SFO compared with the rest of the country?
78.2% of flights arrive on time here against a national 77.3%, 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 92.9% on time. The 5pm–8pm window is the weakest at 64.0%, 29 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
- IAH to ORD, a related route75.1%
- LAX to SFO, a related route60.1%
- IAH to DFW, a related route76.4%
- United Airlines on-time record78.2%
- The best time of day to fly, according to 7.05 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.
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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.