Carrier route record
UAMIA→ORD
United Airlines · Miami to Chicago
- Flights
- 1,040
- 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 MIA to ORD sits in the middle of the pack with a C+. About seven flights in ten arrive on time by the DOT's definition, 7 points worse than the national rate of 77.6%. The late ones land an hour and a half behind schedule. That rests on 1,040 flights, with a median arrival 2 minutes early.
The national on-time rate over the same period is 77.6%, so United on MIA to ORD runs 7 points behind the country as a whole. Across a thousand flights that is about 69 extra late arrivals.
Key figures
On time
70.7%
Arrivals under 15 minutes late, of 1,024 completed flights
Avg delay
85 min
Across delayed arrivals only, not all flights
Cancelled
0.87%
National rate is 1.81%
Whole route
70.8%
Every carrier on MIA to ORD, 4,447 flights
These figures cover 1,040 flights between July 2025 and June 2026. Beyond the headline rate, 11.8% 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.
Carrier by carrier
United against every carrier on MIA to ORD
United flew 1,040 of the 4,447 flights on MIA to ORD, about 23% of it. Its 70.7% on time is about level with the route as a whole at 70.8%. Ranked by on-time rate it is number three of four carriers on the route, where the range runs from Frontier at 73.3% to Spirit at 63.2%. 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 |
|---|---|---|---|---|---|
| Frontier Airlinesthin sample | 46 | 73.3% | 175 min | 2.17% | C |
| American Airlines | 3,015 | 71.6% | 71 min | 1.86% | C |
| United Airlines (this page) | 1,040 | 70.7% | 85 min | 0.87% | C+ |
| Spirit Airlinesthin sample | 346 | 63.2% | 70 min | 6.07% | D− |
Flight by flight
United flight numbers on MIA to ORD
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 37 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–8am55 flights89.1%
- 8am–11am122 flights91.0%
- 11am–2pm333 flights79.5%
- 2pm–5pm422 flights59.7%
- 5pm–8pm108 flights53.8%
- 8pm–5am—
Scale runs 45% to 95%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 53.8% on time, against 91.0% for the 8am–11am 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 2pm–5pm window is the busiest, with 422 flights scheduled in it.
Across the year
United on MIA to ORD through the year
July is the worst month at 57.4% on time, 28 points below April, the best at 85.4%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck. March was the busiest month here, with 138 flights.
Across the week, Wednesday is the strongest day at 76.2% on time and Sunday the weakest at 64.7%. 12 points is a smaller lever than departure hour, but it is free.
Delay causes
Why United runs late on this route
One category carries most of the weight here. National Airspace System accounts for 47% of the 25,000 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.
- 47%National Airspace System
- 30%Late-arriving aircraft
- 17%Carrier
- 6%Extreme weather
47% 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 12,000 minutes out of 25,000, against a national NAS share of 21%. The split is drawn from 25,340 reported delay minutes.
The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 91.0% on time here.
Cancellations are rare at 0.87%, 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
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 11.8% 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 1,197 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 73.7% on time across 1,041 flights, 3 points above 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. 1,040 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 MIA to ORD
Put together: treat all of this as provisional. 1,040 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 70.7% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 1,024 completed flights over 12 months sit behind that.
Related
Where to go next
- MIA to ORD, every carrier
- United on ORD to MIA, the return leg
- American Airlines on MIA to ORD71.6%
- Spirit Airlines on MIA to ORD63.2%
- United Airlines network-wide record
- Miami International (MIA) delay statistics
- Chicago O'Hare International (ORD) delay statistics
- How often a connection fails at the major US hubs
- The best time of day to fly, according to 7.04 million flight records
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.