Flight number record
UA 1666
United Airlines · Cincinnati to Denver
- Route
- CVG → DEN
- Departs
- 09:00
- Flights
- 364
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s UA 1666, check with United Airlines.
UA 1666 earns an A+. Close to nine flights in ten arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 11 points better than the national rate of 77.3%. When something does go wrong the average delay runs an hour and a half. That rests on 364 flights, with a median arrival 10 minutes early.
Set against the rest of the country, UA 1666's record is 11 points better than the US average of 77.3%. That gap is worth roughly 105 fewer late arrivals for every thousand flights.
Key figures
On time
87.8%
Arrivals under 15 minutes late, of 361 completed flights
Avg delay
90 min
Across delayed arrivals only, not all flights
Cancelled
0.82%
National rate is 1.89%
1 hour+ late
5.0%
National rate is 8.3%
These figures cover 364 flights between September 2025 and August 2026. The median arrival is 10 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 1666 flies
UA 1666 flies CVG to DEN without a single fixed slot. Its most common scheduled departure was 09:00, used on 165 of 364 flights, with 08:00 (146 flights) next.
- Departs 09:00165 flights45.3%
- Departs 08:00146 flights40.1%
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 09:00 departure sits in the 8am–11am window. Across every US flight scheduled in that window the on-time rate is 83.9%, and UA 1666 runs 4 points better at 87.8%. Early departures usually start with an aircraft that has not flown yet that day, which is most of why the window does well.
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Against the route
UA 1666 next to CVG to DEN
Every carrier on CVG to DEN combined arrived on time 82.7% of the time across 1,498 flights, so UA 1666 is 5 points ahead of it. United flew 727 flights on the same city pair under all its flight numbers, including this one, and those ran 87.2% on time. Across its whole network United Airlines managed 78.8%, which this flight beats by 9 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| UA 1666thin sample | 364 | 87.8% | 90 min | 0.82% | A+ |
| All United Airlines on CVG–DEN | 727 | 87.2% | 78 min | 0.55% | A+ |
| All carriers on CVG–DEN | 1,498 | 82.7% | 70 min | 0.80% | B+ |
| United Airlines, whole network | 830,825 | 78.8% | 73 min | 1.02% | B |
Across the year
UA 1666 quarter by quarter
UA 1666 did not run the same all year. Its best quarter was Jul–Sep 2025 at 93.3% on time and its weakest Jan–Mar 2026 at 79.8%, a swing of 14 points on roughly 73 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 flights93.3%
- Oct–Dec 202591 flights87.9%
- Jan–Mar 202690 flights79.8%
- Apr–Jun 202691 flights91.0%
- Jul–Sep 202662 flights91.9%
Scale runs 70% to 100%.
By weekday, UA 1666 did best on Sunday at 98.0% on time and worst on Friday at 76.5%. Each day rests on about 52 flights, so a gap of 22 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late UA 1666 runs when it is late
UA 1666 often beats the schedule: 128 of 361 completed flights, 35%, arrived 15 minutes or more early. The 44 late arrivals split 14 under half an hour, 12 between 30 and 60 minutes, and 18 an hour or more.
- 15+ min early128 flights35.5%
- Within 15 min189 flights52.4%
- 15–29 min late14 flights3.9%
- 30–59 min late12 flights3.3%
- 1–2 hours late10 flights2.8%
- 2+ hours late8 flights2.2%
Scale runs 0% to 100%.
Share of 361 completed flights by arrival against schedule.
9 of 36 late departures made up the time and arrived on time, 25% of them. 17 flights left on time and still arrived late.
The worst days
Worst days for UA 1666
The latest arrival of the period was on 16 March 2026, 9 hours 20 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on four of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 16 March 2026 | 9 hours 20 minutes | Carrier |
| 15 May 2026 | 9 hours 18 minutes | Carrier |
| 16 May 2026 | 5 hours 31 minutes | Carrier |
| 2 December 2025 | 5 hours 10 minutes | Late-arriving aircraft |
| 20 October 2025 | 2 hours 21 minutes | Carrier |
Delay causes
Why UA 1666 runs late
Carrier accounts for 65% of the 3,952 delay minutes carriers reported here, and the remaining four split what is left.
- 65%Carrier
- 26%National Airspace System
- 8%Late-arriving aircraft
- 1%Extreme weather
The largest share of delay minutes, 65%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 2,583 of the 3,952 delay minutes reported here. The split is drawn from 3,952 delay minutes reported on UA 1666.
Cancellations are rare at 0.82%, 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 routes
What a delay on this flight costs
5.0% 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 an hour and a half, which a normal layover absorbs.
The 1,069 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 two other city pairs in the data, including DEN to CLT (33) and XNA to DEN (1), but none flew often enough under UA 1666 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to CVG to DEN only.
One caution: this is a thin sample. 364 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 1666
For a booking, UA 1666 has one of the better records a US domestic flight can show: 87.8% on time and 0.82% cancelled. That is a base rate, not a promise about any single day.
Related
Where to go next
- CVG to DEN, every carrier and departure
- DEN to CVG, the return direction
- United Airlines 479 on the same route86.6%
- Frontier Airlines 3725 on the same route81.8%
- Cincinnati/Northern Kentucky International (CVG) 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
- Worst months to fly in the US, ranked by the data
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.