Flight number record
UA 1638
United Airlines · Denver to Los Angeles
- Route
- DEN → LAX
- Departs
- 08:00
- Flights
- 365
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s UA 1638, check with United Airlines.
UA 1638 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 15 points better than the national rate of 77.3%. When something does go wrong the average delay runs about 30 minutes. That rests on 365 flights, with a median arrival 5 minutes early.
Set against the rest of the country, UA 1638's record is 15 points better than the US average of 77.3%. That gap is worth roughly 145 fewer late arrivals for every thousand flights.
Key figures
On time
91.8%
Arrivals under 15 minutes late, of 365 completed flights
Avg delay
30 min
Across delayed arrivals only, not all flights
Cancelled
0.00%
National rate is 1.89%
1 hour+ late
0.5%
National rate is 8.3%
These figures cover 365 flights between September 2025 and August 2026. The median arrival is 5 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 1638 flies
UA 1638 flies DEN to LAX without a single fixed slot. Its most common scheduled departure was 08:00, used on 152 of 365 flights, with 07:50 (56 flights) and 07:45 (48 flights) next.
- Departs 08:00152 flights41.6%
- Departs 07:5056 flights15.3%
- Departs 07:4548 flights13.2%
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 08:00 departure sits in the 8am–11am window. Across every US flight scheduled in that window the on-time rate is 83.9%, and UA 1638 runs 8 points better at 91.8%. 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 1638 next to DEN to LAX
Every carrier on DEN to LAX combined arrived on time 78.7% of the time across 7,708 flights, so UA 1638 is 13 points ahead of it. United flew 3,079 flights on the same city pair under all its flight numbers, including this one, and those ran 84.0% on time. Across its whole network United Airlines managed 78.8%, which this flight beats by 13 points.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| UA 1638 | 365 | 91.8% | 30 min | 0.00% | A+ |
| All United Airlines on DEN–LAX | 3,079 | 84.0% | 56 min | 0.00% | B+ |
| All carriers on DEN–LAX | 7,708 | 78.7% | 63 min | 0.53% | B+ |
| United Airlines, whole network | 830,825 | 78.8% | 73 min | 1.02% | B |
Across the year
UA 1638 quarter by quarter
Quarter by quarter UA 1638 held fairly steady: 90.0% in Jul–Sep 2025, 88.0% in Oct–Dec 2025, 91.1% in Jan–Mar 2026, 94.5% in Apr–Jun 2026 and 95.2% in Jul–Sep 2026. A spread of 7 points is about what a sample of this size moves on its own, so the annual figure is a fair summary.
- Jul–Sep 202530 flights90.0%
- Oct–Dec 202592 flights88.0%
- Jan–Mar 202690 flights91.1%
- Apr–Jun 202691 flights94.5%
- Jul–Sep 202662 flights95.2%
Scale runs 80% to 100%.
By weekday, UA 1638 ranged from 86.5% on Sunday to 96.2% on Wednesday. With about 52 flights behind each day, a spread of 10 points is inside normal variation, so the day you fly is not worth changing for this flight.
Arrival by arrival
How late UA 1638 runs when it is late
Most of the lateness is short. 21 of the 30 late arrivals were under half an hour behind, and 2 reached an hour or more. Not one arrived two hours late.
- 15+ min early86 flights23.6%
- Within 15 min249 flights68.2%
- 15–29 min late21 flights5.8%
- 30–59 min late7 flights1.9%
- 1–2 hours late2 flights0.5%
- 2+ hours late0 flights0.0%
Scale runs 0% to 100%.
Share of 365 completed flights by arrival against schedule.
Only 14 of 365 completed flights left 15 minutes late or more, too few to say how often the time is made up.
The worst days
Worst days for UA 1638
The latest arrival of the period was on 14 December 2025, 1 hour 59 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. The five worst days are spread across December, November, May and September, with no single month standing out.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 14 December 2025 | 1 hour 59 minutes | Late-arriving aircraft |
| 15 November 2025 | 1 hour 2 minutes | Carrier |
| 3 May 2026 | 55 minutes | Late-arriving aircraft |
| 28 December 2025 | 47 minutes | National Airspace System |
| 26 September 2025 | 46 minutes | Carrier |
Delay causes
Why UA 1638 runs late
National Airspace System accounts for 57% of the 900 delay minutes carriers reported here, and the remaining four split what is left.
- 57%National Airspace System
- 22%Carrier
- 20%Late-arriving aircraft
57% 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 516 minutes out of 900, against a national NAS share of 21%. The split is drawn from 900 delay minutes reported on UA 1638.
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
Badly late arrivals are rare here: only 0.5% 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.
The 862 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.
Every one of the 365 flights under UA 1638 in the data flew DEN to LAX. The number was not reused on any other city pair, which makes this a clean record of one route.
One caution: this is a thin sample. 365 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 1638
For a booking, UA 1638 has one of the better records a US domestic flight can show: 91.8% on time and 0.00% cancelled. That is a base rate, not a promise about any single day.
Related
Where to go next
- DEN to LAX, every carrier and departure
- LAX to DEN, the return direction
- United Airlines 1013 on the same route83.8%
- United Airlines 405 on the same route91.2%
- United Airlines 2240 on the same route75.3%
- United Airlines 531 on the same route76.3%
- United Airlines 1195 on the same route82.5%
- Frontier Airlines 4345 on the same route74.9%
- Denver International (DEN) delay statistics
- Los Angeles International (LAX) 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.