Flight number record
UA 1231
United Airlines · Chicago to Houston
- Route
- ORD → IAH
- Departs
- 07:35
- Flights
- 270
- Period
- September 2025 to August 2026
Historical statistics for September 2025 to August 2026, not live status. For today’s UA 1231, check with United Airlines.
UA 1231 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 14 points better than the national rate of 77.3%. When something does go wrong the average delay runs about an hour. That rests on 270 flights, with a median arrival 16 minutes early.
Set against the rest of the country, UA 1231's record is 14 points better than the US average of 77.3%. That gap is worth roughly 141 fewer late arrivals for every thousand flights.
Key figures
On time
91.4%
Arrivals under 15 minutes late, of 266 completed flights
Avg delay
67 min
Across delayed arrivals only, not all flights
Cancelled
1.48%
National rate is 1.89%
1 hour+ late
1.9%
National rate is 8.3%
These figures cover 270 flights between September 2025 and August 2026. The median arrival is 16 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 1231 flies
UA 1231 flies ORD to IAH without a single fixed slot. Its most common scheduled departure was 07:35, used on 125 of 270 flights, with 07:30 (109 flights) and 07:10 (36 flights) next.
- Departs 07:35125 flights46.3%
- Departs 07:30109 flights40.4%
- Departs 07:1036 flights13.3%
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 07:35 departure sits in the 5am–8am window. Across every US flight scheduled in that window the on-time rate is 89.3%, and UA 1231 runs 2 points better at 91.4%. 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 1231 next to ORD to IAH
Every carrier on ORD to IAH combined arrived on time 76.0% of the time across 6,141 flights, so UA 1231 is 15 points ahead of it. United flew 4,080 flights on the same city pair under all its flight numbers, including this one, and those ran 80.0% 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 1231thin sample | 270 | 91.4% | 67 min | 1.48% | A |
| All United Airlines on ORD–IAH | 4,080 | 80.0% | 70 min | 0.66% | B+ |
| All carriers on ORD–IAH | 6,141 | 76.0% | 74 min | 1.40% | B |
| United Airlines, whole network | 830,825 | 78.8% | 73 min | 1.02% | B |
Across the year
UA 1231 quarter by quarter
Quarter by quarter UA 1231 held fairly steady: 92.3% in Oct–Dec 2025, 86.3% in Jan–Mar 2026, 92.2% in Apr–Jun 2026 and 93.3% 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.
- Oct–Dec 202565 flights92.3%
- Jan–Mar 202652 flights86.3%
- Apr–Jun 202691 flights92.2%
- Jul–Sep 202662 flights93.3%
Scale runs 80% to 100%.
By weekday, UA 1231 did best on Tuesday at 97.4% on time and worst on Friday at 81.6%. Each day rests on about 39 flights, so a gap of 16 points is worth noticing but could still narrow in another year.
Arrival by arrival
How late UA 1231 runs when it is late
UA 1231 often beats the schedule: 136 of 266 completed flights, 51%, arrived 15 minutes or more early. The 23 late arrivals split 10 under half an hour, 8 between 30 and 60 minutes, and 5 an hour or more.
- 15+ min early136 flights51.1%
- Within 15 min107 flights40.2%
- 15–29 min late10 flights3.8%
- 30–59 min late8 flights3.0%
- 1–2 hours late1 flights0.4%
- 2+ hours late4 flights1.5%
Scale runs 0% to 100%.
Share of 266 completed flights by arrival against schedule.
Only 15 of 266 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 1231
The latest arrival of the period was on 3 April 2026, 5 hours 47 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. The five worst days are spread across April, March, December and July, with no single month standing out.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 3 April 2026 | 5 hours 47 minutes | Late-arriving aircraft |
| 6 March 2026 | 4 hours 53 minutes | Late-arriving aircraft |
| 16 March 2026 | 2 hours 26 minutes | National Airspace System |
| 29 December 2025 | 2 hours 18 minutes | Carrier |
| 15 July 2026 | 1 hour 9 minutes | Carrier |
Delay causes
Why UA 1231 runs late
Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 1,540 reported delay minutes.
- 40%National Airspace System
- 39%Late-arriving aircraft
- 21%Carrier
- 0%Extreme weather
39% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 1,540 reported delay minutes here, that single category outweighs weather by 39 to one. The split is drawn from 1,540 delay minutes reported on UA 1231.
Cancellations sit at 1.48% 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 1.9% 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 925 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 eight other city pairs in the data, including IAH to EGE (35), LAS to ORD (32) and MIA to EWR (26), but none flew often enough under UA 1231 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to ORD to IAH only.
One caution: this is a thin sample. 270 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 1231
For a booking, UA 1231 has one of the better records a US domestic flight can show: 91.4% on time and 1.48% cancelled. That is a base rate, not a promise about any single day.
Related
Where to go next
- ORD to IAH, every carrier and departure
- IAH to ORD, the return direction
- Frontier Airlines 3135 on the same route78.6%
- American Airlines 3144 on the same route52.5%
- United Airlines 2638 on the same route86.0%
- United Airlines 2426 on the same route72.3%
- Chicago O'Hare International (ORD) delay statistics
- George Bush Intercontinental (IAH) 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.