Flight number record
UA 566
United Airlines · Sacramento to Denver
- Route
- SMF → DEN
- Departs
- 16:19
- Flights
- 308
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s UA 566, check with United Airlines.
UA 566 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 about an hour on average. That rests on 308 flights, with a median arrival 2 minutes early.
Set against the rest of the country, UA 566'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 307 completed flights
Avg delay
56 min
Across delayed arrivals only, not all flights
Cancelled
0.00%
National rate is 1.89%
1 hour+ late
6.2%
National rate is 8.3%
These figures cover 308 flights between September 2025 and August 2026. The median arrival is 2 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 566 flies
UA 566 flies SMF to DEN without a single fixed slot. Its most common scheduled departure was 16:19, used on 75 of 308 flights, with 16:00 (67 flights) and 16:03 (32 flights) next.
- Departs 16:1975 flights24.4%
- Departs 16:0067 flights21.8%
- Departs 16:0332 flights10.4%
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 16:19 departure sits in the 2pm–5pm window. Across every US flight scheduled in that window the on-time rate is 71.9%, and UA 566 runs 12 points better at 83.7%. Midday slots inherit some of the morning's delays without yet carrying the full weight of the evening's.
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Against the route
UA 566 next to SMF to DEN
Every carrier on SMF to DEN combined arrived on time 83.1% of the time across 3,844 flights, so UA 566 is about level with it. United flew 1,791 flights on the same city pair under all its flight numbers, including this one, and those ran 89.0% 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 566thin sample | 308 | 83.7% | 56 min | 0.00% | B+ |
| All United Airlines on SMF–DEN | 1,791 | 89.0% | 71 min | 0.28% | A+ |
| All carriers on SMF–DEN | 3,844 | 83.1% | 57 min | 0.23% | B+ |
| United Airlines, whole network | 830,825 | 78.8% | 73 min | 1.02% | B |
Across the year
UA 566 quarter by quarter
UA 566 did not run the same all year. Its best quarter was Oct–Dec 2025 at 96.1% on time and its weakest Jul–Sep 2026 at 64.4%, a swing of 32 points on roughly 77 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 20256 flights—
- Oct–Dec 202577 flights96.1%
- Jan–Mar 202678 flights82.1%
- Apr–Jun 202687 flights86.2%
- Jul–Sep 202660 flights64.4%
Scale runs 55% to 100%. Rows with fewer than 30 flights show a dash.
By weekday, UA 566 did best on Saturday at 94.9% on time and worst on Thursday at 79.5%. Each day rests on about 44 flights, so a gap of 15 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late UA 566 runs when it is late
The 50 late arrivals split 22 under half an hour, 9 between 30 and 60 minutes, and 19 an hour or more.
- 15+ min early49 flights16.0%
- Within 15 min208 flights67.8%
- 15–29 min late22 flights7.2%
- 30–59 min late9 flights2.9%
- 1–2 hours late14 flights4.6%
- 2+ hours late5 flights1.6%
Scale runs 0% to 100%.
Share of 307 completed flights by arrival against schedule.
6 of 38 late departures made up the time and arrived on time, 16% of them. In the other direction, 18 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 DEN.
The worst days
Worst days for UA 566
The latest arrival of the period was on 6 March 2026, 4 hours 12 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 |
|---|---|---|
| 6 March 2026 | 4 hours 12 minutes | Late-arriving aircraft |
| 22 July 2026 | 3 hours 7 minutes | National Airspace System |
| 7 June 2026 | 2 hours 32 minutes | Late-arriving aircraft |
| 17 July 2026 | 2 hours 24 minutes | Late-arriving aircraft |
| 17 February 2026 | 2 hours 8 minutes | National Airspace System |
Delay causes
Why UA 566 runs late
National Airspace System accounts for 49% of the 2,804 delay minutes carriers reported here, and the remaining four split what is left.
- 49%National Airspace System
- 38%Late-arriving aircraft
- 13%Carrier
38% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 2,804 reported delay minutes here, that single category outweighs weather by 38 to one. The split is drawn from 2,804 delay minutes reported on UA 566.
Cancellations are rare at 0.00%, below the national 1.89% and low enough to earn the plus on the grade. Almost no flights are called off; the risk here is arriving late, not not arriving.
Connections and routes
What a delay on this flight costs
6.2% 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.
The 909 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 same number turns up on six other city pairs in the data, including SFO to DEN (24), EWR to FLL (19) and IAH to BZN (3), but none flew often enough under UA 566 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to SMF to DEN only.
One caution: this is a thin sample. 308 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 566
For a booking, read UA 566 as 83.7% on time with 0.00% cancelled over 308 flights. Those are rates from the past twelve months, not a forecast for any particular day.
Related
Where to go next
- SMF to DEN, every carrier and departure
- DEN to SMF, the return direction
- United Airlines 2285 on the same route97.1%
- United Airlines 1889 on the same route96.4%
- Sacramento International (SMF) delay statistics
- Denver International (DEN) 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.