Route reliability record

SEA→ORD

Seattle to Chicago

Flights: 5,566
Period: July 2025 to June 2026
Distance: 1,721 mi
Carriers: 4

This route sits in the middle of the pack with a B. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.6%. The late ones land a little over an hour behind schedule. That rests on 5,566 flights, of which United Airlines flew 1,534 at 79.8% on time.

United Airlines is the most reliable of the four carriers covered here at 79.8% on time across 1,534 flights.

On time

75.0%

Arrivals under 15 minutes late, of 5,446 completed flights

Avg delay

74 min

Across delayed arrivals only, not all flights

Cancelled

1.28%

National rate is 1.81%

Best carrier

United

79.8% on time across 1,534 flights

These figures cover 5,566 flights between July 2025 and June 2026. Beyond the headline rate, 8.4% 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 SEA to ORD

The choice of carrier is not cosmetic here. United Airlines arrives on time 79.8% of the time; American Airlines manages 71.2%. Sample sizes sit next to every figure, because a two-point gap across 1,336 flights means less than a ten-point one.

On-time performance by carrier on SEA to ORD
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	1,534	79.8%	81 min	0.91%	B+
Delta Air Lines	902	77.5%	71 min	1.22%	B
Alaska Airlines	1,794	72.3%	55 min	1.06%	C
American Airlines	1,336	71.2%	93 min	2.02%	C

United leads American by 9 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.

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 24 points, against 9 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am1,067 flights88.1%
8am–11am913 flights70.1%
11am–2pm1,092 flights67.5%
2pm–5pm744 flights63.7%
5pm–8pm836 flights77.5%
8pm–5am914 flights80.1%

Scale runs 55% to 95%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 88.1% of the time, against 63.7% for the afternoon window. That is 24 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 11am–2pm window is the busiest, with 1,092 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 31 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.February best, August worst

August is the worst month at 60.9% on time, 31 points below February, the best at 92.3%. 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. July was the busiest month here, with 623 flights.

Across the week, Tuesday is the strongest day at 82.9% on time and Sunday the weakest at 68.9%. 14 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 100,000 reported delay minutes.

Carrier
34%
National Airspace System
33%
Late-arriving aircraft
31%
Extreme weather
3%
Security
0%

The largest share of delay minutes, 34%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 34,000 of the 100,000 delay minutes reported here. The split is drawn from 100,152 reported delay minutes.

33% 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 100,000, against a national NAS share of 21%.

Cancellations sit at 1.28% against a national 1.81%, which is ordinary. Diversions add another 0.88%.

Connections and stage length

What a delay here actually costs

8.4% 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 are the a little over an hour kind, which a normal layover absorbs.

At 1,721 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.

The return leg is a different operation and performs like one: it runs 68.5% on time across 5,572 flights, 7 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 7 points of difference.

The sample behind these figures is 5,566 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. February runs 92.3% on time and August 60.9%, a swing of 31 points. If the dates move at all, move them out of August before you think about anything else. 5,446 completed flights over 12 months sit behind that.

Common questions

SEA to ORD questions

How often is SEA to ORD delayed?

About one flight in four arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 25.0% of the 5,566 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 SEA to ORD?

United Airlines leads at 79.8% on time across 1,534 flights. American Airlines is at the other end on 71.2%, a gap of 9 points. 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 SEA to ORD?

The 5am–8am departure window is the strongest at 88.1% on time. The 2pm–5pm window is the weakest at 63.7%, 24 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 August delays on SEA to ORD?

August is the weakest month at 60.9% on time, compared with 92.3% in February. Across the year that is 31 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. SEA to ORD and ORD to SEA 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