Carrier route record
UABOS→ORD
United Airlines · Boston to Chicago
- Flights
- 2,678
- 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 BOS to ORD 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 an hour and a half behind schedule. That rests on 2,678 flights. The strongest carrier on the route with a full sample, Envoy Air, flew 445 at 75.6% on time.
Envoy Air is the most reliable of the five carriers covered here at 75.6% on time across 445 flights.
Key figures
On time
75.0%
Arrivals under 15 minutes late, of 2,617 completed flights
Avg delay
85 min
Across delayed arrivals only, not all flights
Cancelled
1.90%
National rate is 1.81%
Whole route
72.7%
Every carrier on BOS to ORD, 7,637 flights
These figures cover 2,678 flights between July 2025 and June 2026. Beyond the headline rate, 9.9% 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 BOS to ORD
United flew 2,678 of the 7,637 flights on BOS to ORD, about 35% of it. Its 75.0% on time is 2 points better than the route as a whole, which runs 72.7%. Ranked by on-time rate it is number two of six carriers on the route, where the range runs from Envoy at 75.6% to Delta at 65.2%.
The choice of carrier is not cosmetic here. Envoy Air arrives on time 75.6% of the time; Delta Air Lines manages 65.2%. Sample sizes sit next to every figure, because a two-point gap across 962 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Envoy Air | 445 | 75.6% | 91 min | 3.60% | B− |
| United Airlines (this page) | 2,678 | 75.0% | 85 min | 1.90% | B |
| JetBlue Airways | 533 | 73.6% | 68 min | 2.25% | C |
| American Airlines | 2,125 | 73.4% | 93 min | 2.82% | C |
| Republic Airways | 894 | 70.4% | 81 min | 5.93% | C− |
| Delta Air Lines | 962 | 65.2% | 75 min | 3.12% | C− |
Republic Airways cancels 5.9% 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 BOS 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 41 points, against 10 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am578 flights91.0%
- 8am–11am621 flights87.2%
- 11am–2pm475 flights84.3%
- 2pm–5pm526 flights56.2%
- 5pm–8pm344 flights50.3%
- 8pm–5am134 flights51.9%
Scale runs 40% to 95%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 50.3% on time, against 91.0% 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 8am–11am window is the busiest, with 621 flights scheduled in it.
Across the year
United on BOS to ORD through the year
July is the worst month at 66.3% on time, 20 points below February, the best at 86.4%. 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. June was the busiest month here, with 290 flights.
Across the week, Tuesday is the strongest day at 81.6% on time and Sunday the weakest at 68.2%. 13 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 55,000 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
- 33%Late-arriving aircraft
- 17%Carrier
- 3%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 26,000 minutes out of 55,000, against a national NAS share of 21%. The split is drawn from 55,327 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 91.0% on time here.
Cancellations sit at 1.90% against a national 1.81%, which is ordinary. Diversions add another 0.37%.
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. 9.9% 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 68.6% on time across 2,680 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 2,678 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 BOS to ORD
Put together: the calendar is the biggest lever here, not the carrier or the hour. February runs 86.4% on time and July 66.3%, a swing of 20 points. If the dates move at all, move them out of July before you think about anything else. 2,617 completed flights over 12 months sit behind that.
Related
Where to go next
- BOS to ORD, every carrier
- United on ORD to BOS, the return leg
- Envoy Air on BOS to ORD75.6%
- JetBlue Airways on BOS to ORD73.6%
- American Airlines on BOS to ORD73.4%
- Republic Airways on BOS to ORD70.4%
- Delta Air Lines on BOS to ORD65.2%
- United Airlines network-wide record
- Boston Logan International (BOS) delay statistics
- Chicago O'Hare International (ORD) delay statistics
- Why the first flight of the morning is statistically safest
- Same route, different airline: where the carrier you pick matters most
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.