Carrier route record

DLORD→BOS

Delta Air Lines · Chicago to Boston

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 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 77.6%. The late ones land an hour and a half behind schedule. That rests on 962 flights. The strongest carrier on the route with a full sample, Envoy Air, flew 444 at 82.8% on time.

Envoy Air is the most reliable of the five carriers covered here at 82.8% on time across 444 flights.

On time

69.1%

Arrivals under 15 minutes late, of 932 completed flights

Avg delay

88 min

Across delayed arrivals only, not all flights

Cancelled

3.01%

National rate is 1.81%

Whole route

67.6%

Every carrier on ORD to BOS, 7,642 flights

These figures cover 962 flights between July 2025 and June 2026. Beyond the headline rate, 15.5% 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 ORD to BOS

Delta flew 962 of the 7,642 flights on ORD to BOS, about 13% of it. Its 69.1% on time is 2 points better than the route as a whole, which runs 67.6%. Ranked by on-time rate it is number four of six carriers on the route, where the range runs from Envoy at 82.8% to American at 59.9%.

The choice of carrier is not cosmetic here. Envoy Air arrives on time 82.8% of the time; American Airlines manages 59.9%. Sample sizes sit next to every figure, because a two-point gap across 2,126 flights means less than a ten-point one.

On-time performance by carrier on ORD to BOS
Airline	Flights	On time	Avg delay	Cancelled	Grade
Envoy Air	444	82.8%	69 min	2.48%	B
JetBlue Airways	534	73.5%	83 min	2.62%	C
Republic Airways	896	70.3%	73 min	5.47%	C−
Delta Air Lines (this page)	962	69.1%	88 min	3.01%	C−
United Airlines	2,680	68.6%	78 min	1.87%	C
American Airlines	2,126	59.9%	75 min	2.82%	D

Republic Airways cancels 5.5% 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.

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 27 points, against 23 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am250 flights84.1%
8am–11am254 flights73.4%
11am–2pm11 flights—
2pm–5pm218 flights57.9%
5pm–8pm208 flights56.9%
8pm–5am21 flights—

Scale runs 50% to 90%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 56.9% on time, against 84.1% 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 254 flights scheduled in it.

Across the year

Delta on ORD to BOS through the year

Darker means more delays. Figures are on-time percentages.May best, October worst

May is the best month on the calendar at 81.8% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back. October was the busiest month here, with 115 flights.

Across the week, Friday is the strongest day at 74.5% on time and Sunday the weakest at 63.4%. 11 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 25,000 reported delay minutes.

National Airspace System
37%
Late-arriving aircraft
35%
Carrier
27%
Extreme weather
1%

35% 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 25,000 reported delay minutes here, that single category outweighs weather by 28 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 25,441 reported delay minutes.

37% 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 9,342 minutes out of 25,000, against a national NAS share of 21%.

Cancellations run at 3.01%, against 1.81% nationally. That is roughly 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. 15.5% 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 65.2% on time across 962 flights, 4 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 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 ORD to BOS

Put together: the delay figures matter less here than the 3.01% cancellation rate. A late arrival costs you an hour and a half; 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. 932 completed flights over 12 months sit behind that.

Where to go next

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.

Key figures