Carrier route record
DLBOS→ORD
Delta Air Lines · Boston to Chicago
- Flights
- 962
- Period
- July 2025 to June 2026
- Share of route
- 13%
- Carriers
- 6
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Delta Air Lines.
Delta on BOS to ORD draws a C−. About one flight in three arrives at least 15 minutes late, and the typical late arrival is a little over an hour behind schedule. Build slack into anything you connect to. That rests on 962 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
65.2%
Arrivals under 15 minutes late, of 926 completed flights
Avg delay
75 min
Across delayed arrivals only, not all flights
Cancelled
3.12%
National rate is 1.81%
Whole route
72.7%
Every carrier on BOS to ORD, 7,637 flights
These figures cover 962 flights between July 2025 and June 2026. Beyond the headline rate, 15.1% 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
Delta against every carrier on BOS to ORD
Delta flew 962 of the 7,637 flights on BOS to ORD, about 13% of it. Its 65.2% on time is 8 points worse than the route as a whole, which runs 72.7%. Ranked by on-time rate it is last of six carriers on the route, where the range runs from Envoy at 75.6% to Delta at 65.2%.
The five carriers here are closely matched: 5 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Envoy Air | 445 | 75.6% | 91 min | 3.60% | B− |
| United Airlines | 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 (this page) | 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
Delta flight numbers on BOS to ORD
Departure window
When Delta 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 5 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am252 flights79.8%
- 8am–11am12 flights—
- 11am–2pm217 flights74.3%
- 2pm–5pm224 flights60.0%
- 5pm–8pm111 flights39.8%
- 8pm–5am146 flights51.4%
Scale runs 30% to 85%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 39.8% on time, against 79.8% 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 5am–8am window is the busiest, with 252 flights scheduled in it.
Across the year
Delta on BOS to ORD through the year
Delays peak in October, when the on-time rate falls to 51.8%. August is the strongest month at 74.5%. Moving a flexible trip across that boundary buys 23 points. October was the busiest month here, with 115 flights.
Across the week, Friday is the strongest day at 73.6% on time and Sunday the weakest at 54.5%. 19 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Delta 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 24,000 reported delay minutes.
- 39%Late-arriving aircraft
- 32%National Airspace System
- 29%Carrier
- 1%Extreme weather
39% 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 24,000 reported delay minutes here, that single category outweighs weather by 39 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 23,999 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 79.8% on time here.
Cancellations run at 3.12%, against 1.81% nationally. That is about one flight in 30 cancelled outright. A cancelled flight is invisible in every on-time figure on this page, so the punctuality numbers above describe only the flights that actually operated.
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. 15.1% 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 69.1% on time across 962 flights, 4 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 4 points of difference.
One caution: this is a thin sample. 962 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.
What to do with this
Booking Delta on BOS to ORD
Put together: the delay figures matter less here than the 3.12% cancellation rate. A late arrival costs you a little over an hour; a cancelled flight costs you the day. Book the 5am–8am departure so there is still a schedule behind you if it goes wrong, and treat a same-day connection as optimistic. 926 completed flights over 12 months sit behind that.
Related
Where to go next
- BOS to ORD, every carrier
- Delta on ORD to BOS, the return leg
- Envoy Air on BOS to ORD75.6%
- United Airlines on BOS to ORD75.0%
- JetBlue Airways on BOS to ORD73.6%
- American Airlines on BOS to ORD73.4%
- Republic Airways on BOS to ORD70.4%
- Delta Air Lines network-wide record
- Boston Logan International (BOS) delay statistics
- Chicago O'Hare International (ORD) delay statistics
- The US routes with the most cancellations
- Why the first flight of the morning is statistically safest
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.