Flight number record
UA 1665
United Airlines · San Francisco to Boston
- Route
- SFO → BOS
- Departs
- 23:05
- Flights
- 343
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s UA 1665, check with United Airlines.
UA 1665 lands a B, 6 points better than the national rate of 77.3%. About one flight in six arrives 15 minutes late or worse, and those flights are late by roughly 45 minutes on average. That rests on 343 flights, with a median arrival 13 minutes early.
Set against the rest of the country, UA 1665's record is 6 points better than the US average of 77.3%. That gap is worth roughly 64 fewer late arrivals for every thousand flights.
Key figures
On time
83.7%
Arrivals under 15 minutes late, of 338 completed flights
Avg delay
47 min
Across delayed arrivals only, not all flights
Cancelled
1.46%
National rate is 1.89%
1 hour+ late
4.1%
National rate is 8.3%
These figures cover 343 flights between September 2025 and August 2026. The median arrival is 13 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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Schedule
When UA 1665 flies
UA 1665 flies SFO to BOS without a single fixed slot. Its most common scheduled departure was 23:05, used on 82 of 343 flights, with 23:25 (77 flights) and 23:20 (69 flights) next.
- Departs 23:0582 flights23.9%
- Departs 23:2577 flights22.4%
- Departs 23:2069 flights20.1%
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 23:05 departure sits in the 8pm–5am window. Across every US flight scheduled in that window the on-time rate is 70.1%, and UA 1665 runs 14 points better at 83.7%. By that time of day most aircraft have flown several legs already, and whatever went wrong earlier is still in the schedule.
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Against the route
UA 1665 next to SFO to BOS
Every carrier on SFO to BOS combined arrived on time 74.5% of the time across 4,815 flights, so UA 1665 is 9 points ahead of it. United flew 1,939 flights on the same city pair under all its flight numbers, including this one, and those ran 78.5% on time. Across its whole network United Airlines managed 78.8%, which this flight beats by 5 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| UA 1665thin sample | 343 | 83.7% | 47 min | 1.46% | B |
| All United Airlines on SFO–BOS | 1,939 | 78.5% | 73 min | 1.08% | B |
| All carriers on SFO–BOS | 4,815 | 74.5% | 74 min | 1.81% | C |
| United Airlines, whole network | 830,825 | 78.8% | 73 min | 1.02% | B |
Across the year
UA 1665 quarter by quarter
UA 1665 did not run the same all year. Its best quarter was Jul–Sep 2025 at 90.0% on time and its weakest Jan–Mar 2026 at 78.9%, a swing of 11 points on roughly 69 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 flights90.0%
- Oct–Dec 202589 flights82.0%
- Jan–Mar 202675 flights78.9%
- Apr–Jun 202687 flights83.9%
- Jul–Sep 202662 flights88.5%
Scale runs 70% to 95%.
By weekday, UA 1665 did best on Tuesday at 93.5% on time and worst on Sunday at 74.0%. Each day rests on about 49 flights, so a gap of 20 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late UA 1665 runs when it is late
UA 1665 often beats the schedule: 152 of 338 completed flights, 45%, arrived 15 minutes or more early. The 55 late arrivals split 20 under half an hour, 21 between 30 and 60 minutes, and 14 an hour or more.
- 15+ min early152 flights45.0%
- Within 15 min131 flights38.8%
- 15–29 min late20 flights5.9%
- 30–59 min late21 flights6.2%
- 1–2 hours late12 flights3.6%
- 2+ hours late2 flights0.6%
Scale runs 0% to 100%.
Share of 338 completed flights by arrival against schedule.
A late pushback is often recovered here: of 69 departures that left 15 minutes late or more, 28 still arrived on time. 14 flights left on time and still arrived late.
The worst days
Worst days for UA 1665
The latest arrival of the period was on 15 February 2026, 2 hours 31 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. The same cause led on three of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 15 February 2026 | 2 hours 31 minutes | Late-arriving aircraft |
| 5 June 2026 | 2 hours 6 minutes | Carrier |
| 21 February 2026 | 1 hour 56 minutes | Carrier |
| 28 May 2026 | 1 hour 55 minutes | Late-arriving aircraft |
| 17 July 2026 | 1 hour 37 minutes | Late-arriving aircraft |
Delay causes
Why UA 1665 runs late
Late-arriving aircraft accounts for 43% of the 2,565 delay minutes carriers reported here, and the remaining four split what is left.
- 43%Late-arriving aircraft
- 41%Carrier
- 16%National Airspace System
43% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 2,565 reported delay minutes here, that single category outweighs weather by 43 to one. The split is drawn from 2,565 delay minutes reported on UA 1665.
Cancellations sit at 1.46% against a national 1.89%, which is ordinary. Diversions add another 0.00%.
Connections and routes
What a delay on this flight costs
Badly late arrivals are rare here: only 4.1% land an hour or more behind schedule, against 8.3% 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 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 five other city pairs in the data, including ONT to SFO (83), MSY to SFO (55) and SEA to SFO (24), but none flew often enough under UA 1665 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to SFO to BOS only.
One caution: this is a thin sample. 343 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 1665
For a booking, read UA 1665 as 83.7% on time with 1.46% cancelled over 343 flights. Those are rates from the past twelve months, not a forecast for any particular day.
Related
Where to go next
- SFO to BOS, every carrier and departure
- BOS to SFO, the return direction
- Delta Air Lines 400 on the same route88.5%
- JetBlue Airways 734 on the same route74.1%
- JetBlue Airways 1734 on the same route66.2%
- United Airlines 1372 on the same route74.3%
- United Airlines 2647 on the same route81.8%
- United Airlines 2356 on the same route63.0%
- San Francisco International (SFO) delay statistics
- Boston Logan International (BOS) 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
- Why the first flight of the morning is statistically safest
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.