Flight number record
UA 2400
United Airlines · Boston to San Francisco
- Route
- BOS → SFO
- Departs
- 18:10
- Flights
- 310
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s UA 2400, check with United Airlines.
UA 2400 earns an F, which is as low as this site's scale goes for a reason. Only 51.1% of flights arrive inside the 15-minute window, 26 points worse than the national rate of 77.3%. Late arrivals average a little over an hour. Treat any tight connection here as a coin flip. That rests on 310 flights, with a median arrival 13 minutes late.
The national on-time rate over the same period is 77.3%, so UA 2400 runs 26 points behind the country as a whole. Across a thousand flights that is about 262 extra late arrivals.
Key figures
On time
51.1%
Arrivals under 15 minutes late, of 305 completed flights
Avg delay
78 min
Across delayed arrivals only, not all flights
Cancelled
1.61%
National rate is 1.89%
1 hour+ late
21.0%
National rate is 8.3%
These figures cover 310 flights between September 2025 and August 2026. Beyond the headline rate, 21.0% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
Fare search by Aviasales, a Travelpayouts partner. Booking through it may earn this site a commission at no cost to you; it changes no figure here.
Schedule
When UA 2400 flies
UA 2400 flies BOS to SFO without a single fixed slot. Its most common scheduled departure was 18:10, used on 75 of 310 flights, with 18:18 (55 flights) and 18:01 (52 flights) next.
- Departs 18:1075 flights24.2%
- Departs 18:1855 flights17.7%
- Departs 18:0152 flights16.8%
Scale runs 0% to 100%.
Share of scheduled departures at each local time. Times used on fewer than one flight in ten are not listed.
A 18:10 departure sits in the 5pm–8pm window. Across every US flight scheduled in that window the on-time rate is 68.0%, and UA 2400 runs 17 points worse at 51.1%. By that time of day most aircraft have flown several legs already, and whatever went wrong earlier is still in the schedule.
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.
Against the route
UA 2400 next to BOS to SFO
Every carrier on BOS to SFO combined arrived on time 69.2% of the time across 4,817 flights, so UA 2400 is 18 points behind it. United flew 1,940 flights on the same city pair under all its flight numbers, including this one, and those ran 72.5% on time. Across its whole network United Airlines managed 78.8%, which this flight trails by 28 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| UA 2400thin sample | 310 | 51.1% | 78 min | 1.61% | F |
| All United Airlines on BOS–SFO | 1,940 | 72.5% | 66 min | 1.19% | C |
| All carriers on BOS–SFO | 4,817 | 69.2% | 66 min | 1.58% | C |
| United Airlines, whole network | 830,825 | 78.8% | 73 min | 1.02% | B |
Across the year
UA 2400 quarter by quarter
UA 2400 did not run the same all year. Its best quarter was Jan–Mar 2026 at 64.0% on time and its weakest Jul–Sep 2026 at 28.6%, a swing of 35 points on roughly 62 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.
- Jul–Sep 202530 flights56.7%
- Oct–Dec 202588 flights60.9%
- Jan–Mar 202652 flights64.0%
- Apr–Jun 202690 flights44.9%
- Jul–Sep 202650 flights28.6%
Scale runs 20% to 70%.
By weekday, UA 2400 did best on Saturday at 73.0% on time and worst on Monday at 36.2%. Each day rests on about 44 flights, so a gap of 37 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late UA 2400 runs when it is late
The 149 late arrivals split 44 under half an hour, 41 between 30 and 60 minutes, and 64 an hour or more.
- 15+ min early43 flights14.1%
- Within 15 min113 flights37.0%
- 15–29 min late44 flights14.4%
- 30–59 min late41 flights13.4%
- 1–2 hours late37 flights12.1%
- 2+ hours late27 flights8.9%
Scale runs 0% to 100%.
Share of 305 completed flights by arrival against schedule.
24 of 146 late departures made up the time and arrived on time, 16% of them. In the other direction, 27 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 UA 2400
The latest arrival of the period was on 28 July 2026, 17 hours 50 minutes behind schedule; most of its delay minutes were filed as extreme weather. The five worst days are spread across July, April, November and September, with no single month standing out.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 28 July 2026 | 17 hours 50 minutes | Extreme weather |
| 11 April 2026 | 5 hours 51 minutes | Carrier |
| 26 November 2025 | 4 hours 5 minutes | Late-arriving aircraft |
| 24 September 2025 | 3 hours 54 minutes | Late-arriving aircraft |
| 21 July 2026 | 3 hours 54 minutes | Carrier |
Delay causes
Why UA 2400 runs late
National Airspace System accounts for 44% of the 12,000 delay minutes carriers reported here, and the remaining four split what is left.
- 44%National Airspace System
- 30%Late-arriving aircraft
- 18%Carrier
- 9%Extreme weather
44% 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 5,066 minutes out of 12,000, against a national NAS share of 21%. The split is drawn from 11,632 delay minutes reported on UA 2400.
Cancellations sit at 1.61% against a national 1.89%, which is ordinary. Diversions add another 0.00%.
Connections and routes
What a delay on this flight costs
21.0% 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.
At 2,704 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 same number turns up on three other city pairs in the data, including SFO to LAS (144), IAH to BOS (21) and IAH to BNA (1), but none flew often enough under UA 2400 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to BOS to SFO only.
One caution: this is a thin sample. 310 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 UA 2400
For a booking, UA 2400 is a flight to put a long connection behind. 21.0% of its completed flights arrived an hour or more late, which a short layover will not absorb. If the onward flight is on a separate ticket, the risk sits with you.
Related
Where to go next
- BOS to SFO, every carrier and departure
- SFO to BOS, the return direction
- Delta Air Lines 1655 on the same route66.1%
- JetBlue Airways 733 on the same route55.9%
- United Airlines 2441 on the same route84.4%
- JetBlue Airways 333 on the same route54.3%
- United Airlines 1074 on the same route77.8%
- Boston Logan International (BOS) delay statistics
- San Francisco International (SFO) delay statistics
- United Airlines on-time record
- Every United Airlines flight number with a record
- The most and least reliable flight numbers in the US
- How often a connection fails at the major US hubs
A flight number here means United Airlines’s own number as it reports to the DOT. How the figures are computed is on the methodology page.
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.