Carrier route record
UABOS→ORD
United Airlines · Boston to Chicago
- Flights
- 2,791
- Period
- September 2025 to August 2026
- Share of route
- 36%
- Carriers
- 6
Historical statistics for September 2025 to August 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 C. Close to three flights in four arrive on time by the DOT's definition, 3 points worse than the national rate of 77.3%. The late ones land an hour and a half behind schedule. That rests on 2,791 flights. The strongest carrier on the route with a full sample, Envoy Air, flew 441 at 75.7% on time.
Envoy Air is the most reliable of the five carriers covered here at 75.7% on time across 441 flights.
Key figures
On time
74.5%
Arrivals under 15 minutes late, of 2,731 completed flights
Avg delay
86 min
Across delayed arrivals only, not all flights
Cancelled
1.79%
National rate is 1.89%
Whole route
71.9%
Every carrier on BOS to ORD, 7,860 flights
These figures cover 2,791 flights between September 2025 and August 2026. Beyond the headline rate, 10.5% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
United against every carrier on BOS to ORD
United flew 2,791 of the 7,860 flights on BOS to ORD, about 36% of it. Its 74.5% on time is 3 points better than the route as a whole, which runs 71.9%. Ranked by on-time rate it is number two of six carriers on the route, where the range runs from Envoy at 75.7% to Delta at 63.7%.
The choice of carrier is not cosmetic here. Envoy Air arrives on time 75.7% of the time; Delta Air Lines manages 63.7%. Sample sizes sit next to every figure, because a two-point gap across 981 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Envoy Air | 441 | 75.7% | 112 min | 3.40% | B− |
| United Airlines (this page) | 2,791 | 74.5% | 86 min | 1.79% | C |
| American Airlines | 2,165 | 73.3% | 98 min | 2.86% | C |
| Republic Airways | 930 | 71.2% | 82 min | 5.91% | C− |
| JetBlue Airways | 552 | 66.6% | 80 min | 3.26% | C− |
| Delta Air Lines | 981 | 63.7% | 75 min | 3.47% | D− |
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
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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 12 points between the best and worst carrier.
- 5am–8am596 flights89.7%
- 8am–11am697 flights85.7%
- 11am–2pm465 flights83.3%
- 2pm–5pm465 flights56.5%
- 5pm–8pm406 flights51.2%
- 8pm–5am162 flights53.2%
Scale runs 45% to 95%.
The 5pm–8pm window is where this operation falls apart: 51.2% on time, against 89.7% 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 697 flights scheduled in it.
Across the year
United on BOS to ORD through the year
August is the worst month at 63.4% on time, 23 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. August was the busiest month here, with 307 flights.
Across the week, Tuesday is the strongest day at 79.3% on time and Sunday the weakest at 66.6%, a spread of 13 points.
Arrival by arrival
How late United on BOS to ORD runs when it is late
The 697 late arrivals split 221 under half an hour, 190 between 30 and 60 minutes, and 286 an hour or more.
- 15+ min early674 flights24.7%
- Within 15 min1,360 flights49.8%
- 15–29 min late221 flights8.1%
- 30–59 min late190 flights7.0%
- 1–2 hours late138 flights5.1%
- 2+ hours late148 flights5.4%
Scale runs 0% to 100%.
Share of 2,731 completed flights by arrival against schedule.
Time lost at the gate mostly stays lost. Of 484 departures that left 15 minutes late or more, only 49 made it up before arrival. In the other direction, 262 flights left on time yet arrived 15 minutes late or more, so that delay built up after pushback: in the air, in a holding pattern or on the ground at ORD.
The worst days
Worst days for United on BOS to ORD
The latest arrival of the period was on 15 March 2026, 26 hours 54 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on three of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 15 March 2026 | 26 hours 54 minutes | Carrier |
| 15 March 2026 | 21 hours 58 minutes | National Airspace System |
| 3 July 2026 | 19 hours 32 minutes | Carrier |
| 6 November 2025 | 11 hours 59 minutes | Carrier |
| 18 July 2026 | 11 hours 25 minutes | Late-arriving aircraft |
Delay causes
Why United runs late on this route
National Airspace System accounts for 47% of the 60,000 delay minutes carriers reported here, and the remaining four split what is left.
- 47%National Airspace System
- 31%Late-arriving aircraft
- 19%Carrier
- 2%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 28,000 minutes out of 60,000, against a national NAS share of 21%. The split is drawn from 59,775 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 89.7% on time here.
Cancellations sit at 1.79% against a national 1.89%, which is ordinary. Diversions add another 0.36%.
Connections and stage length
What a delay here costs
10.5% of arrivals land a full hour or more behind schedule, against 8.3% nationally. Ninety minutes is the honest minimum for a connection 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.
The return leg is a different operation and performs like one: it runs 68.0% on time across 2,794 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 2,791 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 August 63.4%, a swing of 23 points. If the dates move at all, move them out of August before you think about anything else. 2,731 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 ORD75.7%
- American Airlines on BOS to ORD73.3%
- Republic Airways on BOS to ORD71.2%
- JetBlue Airways on BOS to ORD66.6%
- Delta Air Lines on BOS to ORD63.7%
- United Airlines network-wide record
- Boston Logan International (BOS) delay statistics
- Chicago O'Hare International (ORD) delay statistics
- Same route, different airline: where the carrier you pick matters most
- The best time of day to fly, according to 7.05 million flight records
Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.