Carrier route record
UAORD→MIA
United Airlines · Chicago to Miami
- Flights
- 1,041
- Period
- July 2025 to June 2026
- Share of route
- 23%
- Carriers
- 4
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with United Airlines.
United on ORD to MIA sits in the middle of the pack with a C+. Close to three flights in four arrive on time by the DOT's definition, 4 points worse than the national rate of 77.6%. The late ones land about an hour behind schedule. That rests on 1,041 flights, with a median arrival 4 minutes early.
The US average over the same twelve months is 77.6%, so there is little to separate United on ORD to MIA from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
73.7%
Arrivals under 15 minutes late, of 1,030 completed flights
Avg delay
61 min
Across delayed arrivals only, not all flights
Cancelled
0.58%
National rate is 1.81%
Whole route
74.0%
Every carrier on ORD to MIA, 4,450 flights
These figures cover 1,041 flights between July 2025 and June 2026. The median arrival is 4 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.
Carrier by carrier
United against every carrier on ORD to MIA
United flew 1,041 of the 4,450 flights on ORD to MIA, about 23% of it. Its 73.7% on time is about level with the route as a whole at 74.0%. Ranked by on-time rate it is number two of four carriers on the route, where the range runs from American at 75.6% to Spirit at 61.3%. Two of those carriers flew fewer than 365 flights here, so treat their positions as rough.
Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| American Airlines | 3,015 | 75.6% | 72 min | 1.92% | B |
| United Airlines (this page) | 1,041 | 73.7% | 61 min | 0.58% | C+ |
| Frontier Airlinesthin sample | 46 | 64.4% | 120 min | 2.17% | D |
| Spirit Airlinesthin sample | 348 | 61.3% | 70 min | 6.32% | D− |
Departure window
When United runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 20 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am339 flights83.0%
- 8am–11am313 flights72.3%
- 11am–2pm184 flights70.9%
- 2pm–5pm45 flights64.4%
- 5pm–8pm160 flights62.7%
- 8pm–5am—
Scale runs 55% to 90%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 62.7% on time, against 83.0% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 5am–8am window is the busiest, with 339 flights scheduled in it.
Across the year
United on ORD to MIA through the year
September is the best month on the calendar at 85.4% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. March was the busiest month here, with 138 flights.
Across the week, Tuesday is the strongest day at 83.7% on time and Sunday the weakest at 57.0%. 27 points is a smaller lever than departure hour, but it is free.
Delay causes
Why United runs late on this route
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 17,000 reported delay minutes.
- 37%National Airspace System
- 32%Late-arriving aircraft
- 21%Carrier
- 9%Extreme weather
37% 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 6,195 minutes out of 17,000, against a national NAS share of 21%. The split is drawn from 16,528 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 83.0% on time here.
Cancellations are rare at 0.58%, below the national 1.81% 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 stage length
What a delay here costs
7.8% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says 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 1,197 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 return leg is a different operation and performs like one: it runs 70.7% on time across 1,040 flights, 3 points below this direction. Departure banks, aircraft rotations and the congestion at each end all differ, so scoring the two directions together would average away a real 3 points of difference.
One caution: this is a thin sample. 1,041 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 United on ORD to MIA
Put together: treat all of this as provisional. 1,041 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 73.7% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 1,030 completed flights over 12 months sit behind that.
Related
Where to go next
- ORD to MIA, every carrier
- United on MIA to ORD, the return leg
- American Airlines on ORD to MIA75.6%
- Spirit Airlines on ORD to MIA61.3%
- United Airlines network-wide record
- Chicago O'Hare International (ORD) delay statistics
- Miami International (MIA) delay statistics
- The best time of day to fly, according to 7.04 million flight records
- Worst months to fly in the US, ranked by the data
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.