Carrier route record

UAORD→BOS

United Airlines · Chicago to Boston

Flights: 2,680
Period: July 2025 to June 2026
Share of route: 35%
Carriers: 6

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with United Airlines.

United on ORD to BOS sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 9 points worse than the national rate of 77.6%. The late ones land a little over an hour behind schedule. That rests on 2,680 flights. The strongest carrier on the route with a full sample, Envoy Air, flew 444 at 82.8% on time.

Envoy Air is the most reliable of the five carriers covered here at 82.8% on time across 444 flights.

On time

68.6%

Arrivals under 15 minutes late, of 2,625 completed flights

Avg delay

78 min

Across delayed arrivals only, not all flights

Cancelled

1.87%

National rate is 1.81%

Whole route

67.6%

Every carrier on ORD to BOS, 7,642 flights

These figures cover 2,680 flights between July 2025 and June 2026. Beyond the headline rate, 14.1% 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 ORD to BOS

United flew 2,680 of the 7,642 flights on ORD to BOS, about 35% of it. Its 68.6% on time is about level with the route as a whole at 67.6%. Ranked by on-time rate it is number five of six carriers on the route, where the range runs from Envoy at 82.8% to American at 59.9%.

The choice of carrier is not cosmetic here. Envoy Air arrives on time 82.8% of the time; American Airlines manages 59.9%. Sample sizes sit next to every figure, because a two-point gap across 2,126 flights means less than a ten-point one.

On-time performance by carrier on ORD to BOS
Airline	Flights	On time	Avg delay	Cancelled	Grade
Envoy Air	444	82.8%	69 min	2.48%	B
JetBlue Airways	534	73.5%	83 min	2.62%	C
Republic Airways	896	70.3%	73 min	5.47%	C−
Delta Air Lines	962	69.1%	88 min	3.01%	C−
United Airlines (this page)	2,680	68.6%	78 min	1.87%	C
American Airlines	2,126	59.9%	75 min	2.82%	D

Republic Airways cancels 5.5% of what it schedules here, the highest in the table. A cancelled flight never appears in an on-time rate, so read that column alongside the punctuality one rather than after it.

Flight by flight

United flight numbers on ORD to BOS

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 39 points, against 23 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am508 flights92.4%
8am–11am417 flights82.2%
11am–2pm437 flights62.1%
2pm–5pm646 flights53.9%
5pm–8pm430 flights59.0%
8pm–5am242 flights62.8%

Scale runs 45% to 100%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 92.4% of the time, against 53.9% for the afternoon window. That is 39 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 2pm–5pm window is the busiest, with 646 flights scheduled in it.

Across the year

United on ORD to BOS through the year

Darker means more delays. Figures are on-time percentages.February best, September worst

Delays peak in September, when the on-time rate falls to 46.9%. February is the strongest month at 78.7%. Moving a flexible trip across that boundary buys 32 points. June was the busiest month here, with 290 flights.

Across the week, Saturday is the strongest day at 79.5% on time and Thursday the weakest at 62.9%. 17 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 64,000 reported delay minutes.

National Airspace System
42%
Late-arriving aircraft
41%
Carrier
13%
Extreme weather
5%

41% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 64,000 reported delay minutes here, that single category outweighs weather by 9 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 64,284 reported delay minutes.

42% 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 27,000 minutes out of 64,000, against a national NAS share of 21%.

Cancellations sit at 1.87% against a national 1.81%, which is ordinary. Diversions add another 0.19%.

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. 14.1% 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 867 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 75.0% on time across 2,678 flights, 6 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 6 points of difference.

The sample behind these figures is 2,680 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 United on ORD to BOS

Put together: the calendar is the biggest lever here, not the carrier or the hour. February runs 78.7% on time and September 46.9%, a swing of 32 points. If the dates move at all, move them out of September before you think about anything else. 2,625 completed flights over 12 months sit behind that.

Where to go next

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.

Key figures