Route reliability record

BOS→ORD

Boston to Chicago

Flights: 7,556
Period: June 2025 to May 2026
Distance: 867 mi
Carriers: 6

This route sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 5 points worse than the national rate of 77.4%. The late ones land an hour and a half behind schedule. That rests on 7,556 flights, of which Envoy Air flew 450 at 75.3% on time.

Envoy Air is the most reliable of the six carriers covered here at 75.3% on time across 450 flights.

On time

72.4%

Arrivals under 15 minutes late, of 7,314 completed flights

Avg delay

82 min

Across delayed arrivals only, not all flights

Cancelled

2.73%

National rate is 1.80%

Best carrier

Envoy

75.3% on time across 450 flights

These figures cover 7,556 flights between June 2025 and May 2026. Beyond the headline rate, 11.9% 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

Which airline is most reliable on BOS to ORD

The choice of carrier is not cosmetic here. Envoy Air arrives on time 75.3% of the time; Delta Air Lines manages 64.7%. Sample sizes sit next to every figure, because a two-point gap across 961 flights means less than a ten-point one.

On-time performance by carrier on BOS to ORD
Airline	Flights	On time	Avg delay	Cancelled	Grade
Envoy Air	450	75.3%	88 min	3.33%	B−
United Airlines	2,631	74.3%	82 min	1.79%	C
JetBlue Airways	536	74.3%	68 min	2.05%	C
American Airlines	2,098	73.2%	93 min	2.62%	C
Republic Airways	880	70.1%	75 min	6.14%	C−
Delta Air Lines	961	64.7%	72 min	2.50%	D

Republic Airways cancels 6.1% 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

The best time of day to leave

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 38 points, against 11 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am1,687 flights87.7%
8am–11am1,119 flights85.2%
11am–2pm1,421 flights79.0%
2pm–5pm1,763 flights62.7%
5pm–8pm1,223 flights50.2%
8pm–5am343 flights52.7%

Scale runs 40% to 95%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 50.2% on time, against 87.7% 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.

Across the year

When delays peak on this route

This route's year swings by 19 points from best month to worst, which is wide. An annual average tells you very little about the week you are actually flying, so read the strip rather than the headline if your dates are fixed.

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

Delays peak in October, when the on-time rate falls to 64.0%. February is the strongest month at 83.4%. Moving a flexible trip across that boundary buys 19 points.

Across the week, Tuesday is the strongest day at 75.7% on time and Sunday the weakest at 68.7%. 7 points is a smaller lever than departure hour, but it is free.

Delay causes

Why this route gets delayed

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 166,000 reported delay minutes.

Late-arriving aircraft
41%
National Airspace System
35%
Carrier
21%
Extreme weather
3%
Security
0%

41% 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 166,000 reported delay minutes here, that single category outweighs weather by 16 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.

35% 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 57,000 minutes out of 166,000, against a national NAS share of 21%.

Cancellations run at 2.73%, against 1.80% nationally. That is roughly one flight in 40 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 actually costs

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 11.9% of arrivals land a full hour or more behind schedule, against 8.2% 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 67.7% on time across 7,561 flights, 5 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 5 points of difference.

The sample behind these figures is 7,556 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 this route

Put together: the calendar is the biggest lever here, not the carrier or the hour. February runs 83.4% on time and October 64.0%, a swing of 19 points. If the dates move at all, move them out of October before you think about anything else.

Common questions

BOS to ORD questions

How often is BOS to ORD delayed?

Roughly one flight in four arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 27.6% of the 7,556 flights in this analysis, against 22.6% nationally. Delayed flights are late by an hour and a half on average.

Which airline is most reliable on BOS to ORD?

Envoy Air leads at 75.3% on time across 450 flights. Delta Air Lines is at the other end on 64.7%, a gap of 11 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.

What time of day has the fewest delays on BOS to ORD?

The 5am–8am departure window is the strongest at 87.7% on time. The 5pm–8pm window is the weakest at 50.2%, 38 points behind. Later departures inherit delays from earlier flights the same aircraft has already flown, which is why the curve slopes the way it does.

How bad are October delays on BOS to ORD?

October is the weakest month at 64.0% on time, compared with 83.4% in February. Across the year that is 19 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.

Where to go next

Direction matters. BOS to ORD and ORD to BOS are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.

Source: US DOT Bureau of Transportation Statistics, on-time performance data, June 2025 to May 2026. Updated monthly. How this data is collected.

Key figures