Carrier route record
UAORD→BOS
United Airlines · Chicago to Boston
- Flights
- 2,794
- 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 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 77.3%. The late ones land a little over an hour behind schedule. That rests on 2,794 flights. The strongest carrier on the route with a full sample, Envoy Air, flew 440 at 82.7% on time.
Envoy Air is the most reliable of the five carriers covered here at 82.7% on time across 440 flights.
Key figures
On time
68.0%
Arrivals under 15 minutes late, of 2,739 completed flights
Avg delay
80 min
Across delayed arrivals only, not all flights
Cancelled
1.79%
National rate is 1.89%
Whole route
66.6%
Every carrier on ORD to BOS, 7,864 flights
These figures cover 2,794 flights between September 2025 and August 2026. Beyond the headline rate, 15.0% 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 ORD to BOS
United flew 2,794 of the 7,864 flights on ORD to BOS, about 36% of it. Its 68.0% on time is about level with the route as a whole at 66.6%. Ranked by on-time rate it is number four of six carriers on the route, where the range runs from Envoy at 82.7% to American at 59.5%.
The choice of carrier is not cosmetic here. Envoy Air arrives on time 82.7% of the time; American Airlines manages 59.5%. Sample sizes sit next to every figure, because a two-point gap across 2,164 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Envoy Air | 440 | 82.7% | 67 min | 2.50% | B |
| Republic Airways | 932 | 69.7% | 79 min | 5.90% | C− |
| JetBlue Airways | 553 | 68.1% | 98 min | 3.98% | C− |
| United Airlines (this page) | 2,794 | 68.0% | 80 min | 1.79% | C |
| Delta Air Lines | 981 | 67.4% | 90 min | 3.47% | C− |
| American Airlines | 2,164 | 59.5% | 78 min | 2.91% | 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 ORD to BOS
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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 40 points, against 23 points between the best and worst carrier.
- 5am–8am520 flights92.4%
- 8am–11am488 flights81.9%
- 11am–2pm424 flights58.7%
- 2pm–5pm649 flights52.8%
- 5pm–8pm443 flights56.1%
- 8pm–5am270 flights65.8%
Scale runs 45% to 100%.
Book the early departure. Flights leaving between 5am–8am arrive on time 92.4% of the time, against 52.8% for the afternoon window. That is 40 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 649 flights scheduled in it.
Across the year
United on ORD to BOS through the year
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. August was the busiest month here, with 308 flights.
Across the week, Saturday is the strongest day at 76.0% on time and Thursday the weakest at 65.6%, a spread of 10 points.
Arrival by arrival
How late United on ORD to BOS runs when it is late
The 876 late arrivals split 211 under half an hour, 253 between 30 and 60 minutes, and 412 an hour or more.
- 15+ min early651 flights23.8%
- Within 15 min1,212 flights44.2%
- 15–29 min late211 flights7.7%
- 30–59 min late253 flights9.2%
- 1–2 hours late237 flights8.7%
- 2+ hours late175 flights6.4%
Scale runs 0% to 100%.
Share of 2,739 completed flights by arrival against schedule.
102 of 828 late departures made up the time and arrived on time, 12% of them. In the other direction, 150 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 BOS.
The worst days
Worst days for United on ORD to BOS
The latest arrival of the period was on 29 November 2025, 9 hours 23 minutes behind schedule; most of its delay minutes were filed as a late-arriving aircraft. The same cause led on five of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 29 November 2025 | 9 hours 23 minutes | Late-arriving aircraft |
| 27 April 2026 | 9 hours 16 minutes | Late-arriving aircraft |
| 25 September 2025 | 7 hours 54 minutes | Late-arriving aircraft |
| 17 June 2026 | 7 hours 20 minutes | Late-arriving aircraft |
| 25 September 2025 | 7 hours 6 minutes | Late-arriving aircraft |
Delay causes
Why United runs late on this route
National Airspace System accounts for 44% of the 70,000 delay minutes carriers reported here, and the remaining four split what is left.
- 44%National Airspace System
- 40%Late-arriving aircraft
- 12%Carrier
- 4%Extreme weather
40% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 70,000 reported delay minutes here, that single category outweighs weather by 9 to one. The split is drawn from 70,198 reported delay minutes.
44% 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 31,000 minutes out of 70,000, against a national NAS share of 21%.
Cancellations sit at 1.79% against a national 1.89%, which is ordinary. Diversions add another 0.18%.
Connections and stage length
What a delay here costs
15.0% 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 74.5% on time across 2,791 flights, 7 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 7 points of difference.
The sample behind these figures is 2,794 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. 2,739 completed flights over 12 months sit behind that.
Related
Where to go next
- ORD to BOS, every carrier
- United on BOS to ORD, the return leg
- Envoy Air on ORD to BOS82.7%
- Republic Airways on ORD to BOS69.7%
- JetBlue Airways on ORD to BOS68.1%
- Delta Air Lines on ORD to BOS67.4%
- American Airlines on ORD to BOS59.5%
- United Airlines network-wide record
- Chicago O'Hare International (ORD) delay statistics
- Boston Logan International (BOS) 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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.