Route reliability record

MIA→ORD

Miami to Chicago

Flights: 4,447
Period: July 2025 to June 2026
Distance: 1,197 mi
Carriers: 4

This route 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 a little over an hour behind schedule. That rests on 4,447 flights, of which American Airlines flew 3,015 at 71.6% on time.

The national on-time rate over the same period is 77.6%, so this route runs 7 points behind the country as a whole. Across a thousand flights that is about 68 extra late arrivals.

On time

70.8%

Arrivals under 15 minutes late, of 4,315 completed flights

Avg delay

75 min

Across delayed arrivals only, not all flights

Cancelled

1.96%

National rate is 1.81%

Best carrier

American

71.6% on time across 3,015 flights

These figures cover 4,447 flights between July 2025 and June 2026. Beyond the headline rate, 11.0% 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

Which airline is most reliable on MIA to ORD

The two carriers here are closely matched: about a point separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.

On-time performance by carrier on MIA to ORD
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	1,040	70.7%	85 min	0.87%	C+
Spirit Airlinesthin sample	346	63.2%	70 min	6.07%	D−

No carrier stands out. American tops the table at 71.6%, about a point clear of the bottom, which is inside the range this kind of sample moves year to year.

Departure window

The best time of day to leave

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 31 points, against about a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am568 flights85.6%
8am–11am735 flights85.5%
11am–2pm609 flights78.6%
2pm–5pm1,097 flights60.3%
5pm–8pm701 flights54.9%
8pm–5am737 flights68.8%

Scale runs 45% to 90%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 54.9% on time, against 85.6% 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 2pm–5pm window is the busiest, with 1,097 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 21 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.

Darker means more delays. Figures are on-time percentages.November best, July worst

July is the worst month at 56.7% on time, 21 points below November, the best at 77.7%. 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 498 flights.

Across the week, Tuesday is the strongest day at 76.8% on time and Sunday the weakest at 61.7%. 15 points is a smaller lever than departure hour, but it is free.

Delay causes

Why this route gets delayed

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 95,000 reported delay minutes.

National Airspace System
35%
Late-arriving aircraft
32%
Carrier
26%
Extreme weather
7%
Security
0%

35% 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 33,000 minutes out of 95,000, against a national NAS share of 21%. The split is drawn from 94,549 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 85.6% on time here.

Cancellations sit at 1.96% against a national 1.81%, which is ordinary. Diversions add another 1.01%.

Connections and stage length

What a delay here actually costs

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 11.0% 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 74.0% on time across 4,450 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.

The sample behind these figures is 4,447 flights, enough that the headline rate is stable to within roughly a point. The hour-block and month splits divide that further, so read the thinner bars with more caution than the headline.

What to do with this

Booking this route

Put together: the calendar is the biggest lever here, not the carrier or the hour. November runs 77.7% on time and July 56.7%, a swing of 21 points. If the dates move at all, move them out of July before you think about anything else. 4,315 completed flights over 12 months sit behind that.

Common questions

MIA to ORD questions

How often is MIA to ORD delayed?

Roughly one flight in three arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 29.2% of the 4,447 flights in this analysis, against 22.4% nationally. Delayed flights are late by a little over an hour on average.

Which airline is most reliable on MIA to ORD?

American Airlines leads at 71.6% on time across 3,015 flights. United Airlines is at the other end on 70.7%, a gap of about a point. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.

What time of day has the fewest delays on MIA to ORD?

The 5am–8am departure window is the strongest at 85.6% on time. The 5pm–8pm window is the weakest at 54.9%, 31 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.

How bad are July delays on MIA to ORD?

July is the weakest month at 56.7% on time, compared with 77.7% in November. Across the year that is 21 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.

Where to go next

Direction matters. MIA to ORD and ORD to MIA are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.

Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Updated monthly. How this data is collected.

Key figures