Flight number record
UA 1240
United Airlines · Dallas-Fort Worth to Washington
- Route
- DFW → IAD
- Departs
- 17:20
- Flights
- 328
- Period
- July 2025 to June 2026
Historical statistics for July 2025 to June 2026, not live status. For today’s UA 1240, check with United Airlines.
UA 1240 lands a B, 2 points better than the national rate of 77.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by an hour and a half on average. That is a workable record, not a spotless one. That rests on 328 flights, with a median arrival 5 minutes early.
Key figures
On time
79.9%
Arrivals under 15 minutes late, of 324 completed flights
Avg delay
84 min
Across delayed arrivals only, not all flights
Cancelled
1.22%
National rate is 1.81%
1 hour+ late
10.8%
National rate is 8.1%
These figures cover 328 flights between July 2025 and June 2026. Beyond the headline rate, 10.8% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.
Schedule
When UA 1240 flies
UA 1240 flies DFW to IAD without a single fixed slot. Its most common scheduled departure was 17:20, used on 86 of 328 flights, with 17:22 (57 flights) and 17:25 (52 flights) next. Carriers retime flights through the season, so the rates here blend slightly different positions in the aircraft's day.
- Departs 17:2086 flights26.2%
- Departs 17:2257 flights17.4%
- Departs 17:2552 flights15.9%
Scale runs 0% to 100%. Rows with fewer than 30 flights show a dash.
Share of scheduled departures at each local time. Times used on fewer than one flight in ten are not listed.
A 17:20 departure sits in the 5pm–8pm window. Across every US flight scheduled in that window the on-time rate is 68.2%, and UA 1240 runs 12 points better at 79.9%. By that time of day most aircraft have flown several legs already, and whatever went wrong earlier is still in the schedule.
Against the route
UA 1240 next to DFW to IAD
Every carrier on DFW to IAD combined arrived on time 78.2% of the time across 1,928 flights, so UA 1240 is 2 points ahead of it. United flew 915 flights on the same city pair under all its flight numbers, including this one, and those ran 84.4% on time. Across its whole network United Airlines managed 79.0%, close to this flight's figure.
| Compared with | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| UA 1240thin sample | 328 | 79.9% | 84 min | 1.22% | B |
| All United Airlines on DFW–IAD | 915 | 84.4% | 93 min | 0.98% | B+ |
| All carriers on DFW–IAD | 1,928 | 78.2% | 80 min | 2.28% | B |
| United Airlines, whole network | 821,041 | 79.0% | 72 min | 1.01% | B |
Across the year
UA 1240 quarter by quarter
UA 1240 did not run the same all year. Its best quarter was Jan–Mar 2026 at 86.1% on time and its weakest Apr–Jun 2026 at 75.6%, a swing of 11 points on roughly 82 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 202592 flights82.4%
- Oct–Dec 202571 flights76.1%
- Jan–Mar 202674 flights86.1%
- Apr–Jun 202691 flights75.6%
Scale runs 65% to 90%. Rows with fewer than 30 flights show a dash.
By weekday, UA 1240 ranged from 75.0% on Sunday to 84.1% on Monday. With about 47 flights behind each day, a spread of 9 points is inside normal variation, so the day you fly is not worth changing for this flight.
Delay causes
Why UA 1240 runs late
One category carries most of the weight here. Late-arriving aircraft accounts for 45% of the 5,480 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.
- 45%Late-arriving aircraft
- 32%Carrier
- 20%National Airspace System
- 3%Extreme weather
45% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 5,480 reported delay minutes here, that single category outweighs weather by 14 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 5,480 delay minutes reported on UA 1240.
Cancellations sit at 1.22% against a national 1.81%, which is ordinary. Diversions add another 0.00%.
Connections and routes
What a delay on this flight costs
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 10.8% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.
The 1,172 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. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.
The same number turns up on two other city pairs in the data, including ORD to FCA (19) and SFO to EWR (1), but none flew often enough under UA 1240 to report a rate for. Carriers move flight numbers between routes, so the figures on this page apply to DFW to IAD only.
One caution: this is a thin sample. 328 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 1240
For a booking, read UA 1240 as 79.9% on time with 1.22% cancelled over 328 flights. Those are rates from the past twelve months, not a forecast for any particular day.
Related
Where to go next
- DFW to IAD, every carrier and departure
- IAD to DFW, the return direction
- United Airlines 358 on the same route85.7%
- United Airlines 2639 on the same route88.2%
- Dallas/Fort Worth International (DFW) delay statistics
- Washington Dulles International (IAD) 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, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.