Carrier route record
DLBOS→ORD
Delta Air Lines · Boston to Chicago
- Flights
- 981
- Period
- September 2025 to August 2026
- Share of route
- 12%
- Carriers
- 6
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with Delta Air Lines.
Delta on BOS to ORD carries a cancellation problem, not just a delay problem: 3.5% of scheduled flights never operate, against 1.9% nationally. Of the ones that do fly, about two flights in three arrive on time, worth a D− overall. The punctuality figure counts only flights that actually departed, so it flatters an operation that cancels this often. That rests on 981 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
63.7%
Arrivals under 15 minutes late, of 941 completed flights
Avg delay
75 min
Across delayed arrivals only, not all flights
Cancelled
3.47%
National rate is 1.89%
Whole route
71.9%
Every carrier on BOS to ORD, 7,860 flights
These figures cover 981 flights between September 2025 and August 2026. Beyond the headline rate, 16.2% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
Delta against every carrier on BOS to ORD
Delta flew 981 of the 7,860 flights on BOS to ORD, about 12% of it. Its 63.7% on time is 8 points worse than the route as a whole, which runs 71.9%. Ranked by on-time rate it is last 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; JetBlue Airways manages 66.6%. Sample sizes sit next to every figure, because a two-point gap across 552 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 | 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 (this page) | 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
Delta flight numbers on BOS to ORD
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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 44 points, against 9 points between the best and worst carrier.
- 5am–8am264 flights80.8%
- 8am–11am6 flights—
- 11am–2pm231 flights71.4%
- 2pm–5pm221 flights59.7%
- 5pm–8pm107 flights36.5%
- 8pm–5am152 flights45.9%
Scale runs 30% to 85%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 36.5% on time, against 80.8% 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 264 flights scheduled in it.
Across the year
Delta on BOS to ORD through the year
May is the best month on the calendar at 74.3% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. August was the busiest month here, with 119 flights.
Across the week, Wednesday is the strongest day at 72.4% on time and Sunday the weakest at 51.5%, a spread of 21 points.
Arrival by arrival
How late Delta on BOS to ORD runs when it is late
The 342 late arrivals split 87 under half an hour, 103 between 30 and 60 minutes, and 152 an hour or more.
- 15+ min early225 flights23.9%
- Within 15 min374 flights39.7%
- 15–29 min late87 flights9.2%
- 30–59 min late103 flights10.9%
- 1–2 hours late93 flights9.9%
- 2+ hours late59 flights6.3%
Scale runs 0% to 100%.
Share of 941 completed flights by arrival against schedule.
Time lost at the gate mostly stays lost. Of 294 departures that left 15 minutes late or more, only 24 made it up before arrival. In the other direction, 72 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 Delta on BOS to ORD
The latest arrival of the period was on 20 September 2025, 6 hours 2 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The five worst days are spread across September, May, April and November, with no single month standing out.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 20 September 2025 | 6 hours 2 minutes | Carrier |
| 9 May 2026 | 5 hours 42 minutes | Carrier |
| 15 April 2026 | 5 hours 32 minutes | Late-arriving aircraft |
| 29 November 2025 | 5 hours 17 minutes | National Airspace System |
| 13 September 2025 | 4 hours 58 minutes | National Airspace System |
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 26,000 reported delay minutes.
- 39%Late-arriving aircraft
- 34%National Airspace System
- 26%Carrier
- 0%Extreme weather
39% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 26,000 reported delay minutes here, that single category outweighs weather by 39 to one. The split is drawn from 25,616 reported delay minutes.
34% 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 8,763 minutes out of 26,000, against a national NAS share of 21%.
Cancellations run at 3.47%, against 1.89% 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
16.2% 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 67.4% on time across 981 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. 981 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 3.47% 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. 941 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 ORD75.7%
- United Airlines on BOS to ORD74.5%
- American Airlines on BOS to ORD73.3%
- Republic Airways on BOS to ORD71.2%
- JetBlue Airways on BOS to ORD66.6%
- 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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.