Route reliability record
SEA→ORD
Seattle to Chicago
- Flights
- 5,555
- Period
- June 2025 to May 2026
- Distance
- 1,721 mi
- Carriers
- 4
This route sits in the middle of the pack with a C. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.4%. The late ones land about an hour behind schedule. That rests on 5,555 flights, of which United Airlines flew 1,539 at 79.6% on time.
United Airlines is the most reliable of the four carriers covered here at 79.6% on time across 1,539 flights.
Key figures
On time
74.8%
Arrivals under 15 minutes late, of 5,444 completed flights
Avg delay
68 min
Across delayed arrivals only, not all flights
Cancelled
1.17%
National rate is 1.80%
Best carrier
United
79.6% on time across 1,539 flights
These figures cover 5,555 flights between June 2025 and May 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
Which airline is most reliable on SEA to ORD
The choice of carrier is not cosmetic here. United Airlines arrives on time 79.6% of the time; American Airlines manages 70.8%. Sample sizes sit next to every figure, because a two-point gap across 1,320 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 1,539 | 79.6% | 72 min | 0.91% | B+ |
| Delta Air Lines | 898 | 77.4% | 68 min | 1.00% | B |
| Alaska Airlines | 1,798 | 72.4% | 52 min | 0.89% | C+ |
| American Airlines | 1,320 | 70.8% | 85 min | 1.97% | 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 23 points, against 9 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am1,061 flights88.3%
- 8am–11am850 flights70.6%
- 11am–2pm1,193 flights66.3%
- 2pm–5pm711 flights65.8%
- 5pm–8pm833 flights78.0%
- 8pm–5am907 flights78.1%
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 88.3% of the time, against 65.8% for the afternoon window. That is 23 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on.
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.
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.
Across the week, Tuesday is the strongest day at 81.6% on time and Sunday the weakest at 69.9%. 12 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 93,000 reported delay minutes.
- 33%Carrier
- 33%Late-arriving aircraft
- 31%National Airspace System
- 3%Extreme weather
- 0%Security
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 88.3% on time here.
No single cause dominates. carrier at 33%, late-arriving aircraft at 33% and national airspace system at 31% split the 93,000 reported delay minutes between them. An even spread like this usually means the operation is running close to its designed capacity with no one obvious weak point, and it is the hardest pattern for a traveller to route around.
Cancellations sit at 1.17% against a national 1.80%, which is ordinary. Diversions add another 0.83%.
Connections and stage length
What a delay here actually costs
7.9% of arrivals land an hour or more late, close to the national 8.2%. 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 about 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 68.6% on time across 5,561 flights, 6 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 6 points of difference.
The sample behind these figures is 5,555 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.
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 25.2% of the 5,555 flights in this analysis, against 22.6% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on SEA to ORD?
United Airlines leads at 79.6% on time across 1,539 flights. American Airlines is at the other end on 70.8%, 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 88.3% on time. The 2pm–5pm window is the weakest at 65.8%, 23 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.
Related
Where to go next
- ORD to SEA — the return legseparate record
- Seattle-Tacoma International (SEA) delay statistics
- Chicago O'Hare International (ORD) delay statistics
- United Airlines on-time record79.6%
- Delta Air Lines on-time record77.4%
- Alaska Airlines on-time record72.4%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 million flight records
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, June 2025 to May 2026. Updated monthly. How this data is collected.