Carrier route record
UABOI→SFO
United Airlines · Boise to San Francisco
- Flights
- 231
- Period
- September 2025 to August 2026
- Share of route
- 13%
- Carriers
- 2
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with United Airlines.
United on BOI to SFO draws a D+. Roughly one flight in three arrives at least 15 minutes late, and the typical late arrival is close to two hours behind schedule. Build slack into anything you connect to. That rests on 231 flights, with a median arrival 1 minute late.
The national on-time rate over the same period is 77.3%, so United on BOI to SFO runs 16 points behind the country as a whole. Across a thousand flights that is about 160 extra late arrivals.
Key figures
On time
61.3%
Arrivals under 15 minutes late, of 230 completed flights
Avg delay
104 min
Across delayed arrivals only, not all flights
Cancelled
0.43%
National rate is 1.89%
Whole route
65.3%
Every carrier on BOI to SFO, 1,744 flights
These figures cover 231 flights between September 2025 and August 2026. Beyond the headline rate, 22.6% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
United against every carrier on BOI to SFO
United flew 231 of the 1,744 flights on BOI to SFO, about 13% of it. Its 61.3% on time is 4 points worse than the route as a whole, which runs 65.3%. Ranked by on-time rate it is last of two carriers on the route, where the range runs from SkyWest at 66.0% to United at 61.3%.
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 |
|---|---|---|---|---|---|
| SkyWest Airlines | 1,513 | 66.0% | 71 min | 0.40% | C+ |
| United Airlines (this page)thin sample | 231 | 61.3% | 104 min | 0.43% | D+ |
Timetable by Aviasales, a Travelpayouts partner. Booking through it may earn this site a commission at no cost to you; it changes no figure here.
Departure window
When United runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 67 points, against half a point between the best and worst carrier.
- 5am–8am37 flights97.3%
- 8am–11am—
- 11am–2pm—
- 2pm–5pm91 flights82.2%
- 5pm–8pm103 flights30.1%
- 8pm–5am—
Scale runs 20% to 100%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 30.1% on time, against 97.3% 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 5pm–8pm window is the busiest, with 103 flights scheduled in it.
Across the year
United on BOI to SFO through the year
- Jul–Sep 202530 flights86.7%
- Oct–Dec 202598 flights86.6%
- Apr–Jun 202641 flights24.4%
- Jul–Sep 202662 flights33.9%
Scale runs 15% to 90%.
Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 61.3% on time across 231 flights.
United on BOI to SFO did not run the same all year. Its best quarter was Jul–Sep 2025 at 86.7% on time and its weakest Apr–Jun 2026 at 24.4%, a swing of 62 points on roughly 58 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.
Across the week, Tuesday is the strongest day at 75.8% on time and Friday the weakest at 46.9%, a spread of 29 points.
Arrival by arrival
How late United on BOI to SFO runs when it is late
United on BOI to SFO often beats the schedule: 64 of 230 completed flights, 28%, arrived 15 minutes or more early. When United on BOI to SFO is late it tends to be very late: 52 of its 89 late arrivals were an hour or more behind, and 18 were two hours or more.
- 15+ min early64 flights27.8%
- Within 15 min77 flights33.5%
- 15–29 min late15 flights6.5%
- 30–59 min late22 flights9.6%
- 1–2 hours late34 flights14.8%
- 2+ hours late18 flights7.8%
Scale runs 0% to 100%.
Share of 230 completed flights by arrival against schedule.
Time lost at the gate mostly stays lost. Of 85 departures that left 15 minutes late or more, only 8 made it up before arrival. In the other direction, 12 flights left on time yet arrived 15 minutes late or more, so that delay built up after pushback: in the air, in a holding pattern or on the ground at SFO.
The worst days
Worst days for United on BOI to SFO
The latest arrival of the period was on 18 June 2026, 17 hours 7 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). Three of the five worst days fell in June 2026.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 18 June 2026 | 17 hours 7 minutes | Carrier |
| 13 June 2026 | 15 hours 37 minutes | Carrier |
| 21 November 2025 | 9 hours 22 minutes | Late-arriving aircraft |
| 12 November 2025 | 5 hours 15 minutes | Carrier |
| 8 June 2026 | 3 hours 41 minutes | National Airspace System |
Delay causes
Why United runs late on this route
National Airspace System accounts for 47% of the 9,277 delay minutes carriers reported here, and the remaining four split what is left.
- 47%National Airspace System
- 30%Carrier
- 23%Late-arriving aircraft
- 0%Extreme weather
47% 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 4,376 minutes out of 9,277, against a national NAS share of 21%. The split is drawn from 9,277 reported delay minutes.
Cancellations are rare at 0.43%, 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 costs
22.6% of arrivals land a full hour or more behind schedule, against 8.3% nationally. Ninety minutes is the honest minimum for a connection here, and two hours if the onward flight is on a separate ticket.
The 522 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 72.8% on time across 230 flights, 12 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 12 points of difference.
One caution: this is a thin sample. 231 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
What to do with this
Booking United on BOI to SFO
Put together: treat all of this as provisional. 231 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 61.3% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 230 completed flights over 12 months sit behind that.
Related
Where to go next
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.