Route reliability record

ORD→BOS

Chicago to Boston

Flights: 7,561
Period: June 2025 to May 2026
Distance: 867 mi
Carriers: 6

This route draws a C. About one flight in three arrive 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 7,561 flights, of which Envoy Air flew 449 at 82.6% on time.

Envoy Air is the most reliable of the six carriers covered here at 82.6% on time across 449 flights.

On time

67.7%

Arrivals under 15 minutes late, of 7,347 completed flights

Avg delay

78 min

Across delayed arrivals only, not all flights

Cancelled

2.59%

National rate is 1.80%

Best carrier

Envoy

82.6% on time across 449 flights

These figures cover 7,561 flights between June 2025 and May 2026. Beyond the headline rate, 14.3% 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 ORD to BOS

The choice of carrier is not cosmetic here. Envoy Air arrives on time 82.6% of the time; American Airlines manages 60.7%. Sample sizes sit next to every figure, because a two-point gap across 2,100 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	449	82.6%	69 min	2.45%	B
JetBlue Airways	537	73.3%	89 min	2.42%	C
Republic Airways	881	70.9%	76 min	5.45%	C−
Delta Air Lines	961	68.6%	85 min	2.39%	C
United Airlines	2,633	68.3%	78 min	1.75%	C
American Airlines	2,100	60.7%	74 min	2.62%	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

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 32 points, against 22 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am1,524 flights86.3%
8am–11am1,415 flights78.0%
11am–2pm1,112 flights61.7%
2pm–5pm1,389 flights54.6%
5pm–8pm1,424 flights58.3%
8pm–5am697 flights60.5%

Scale runs 45% to 90%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 86.3% of the time, against 54.6% for the afternoon window. That is 32 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on.

Across the year

When delays peak on this route

This route's year swings by 20 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.May best, September worst

May is the best month on the calendar at 76.6% on time. Shoulder season thins the schedule and takes the summer weather with it, and the operation gets its margin back.

Across the week, Saturday is the strongest day at 75.4% on time and Monday the weakest at 64.2%. 11 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 185,000 reported delay minutes.

Late-arriving aircraft
41%
National Airspace System
33%
Carrier
21%
Extreme weather
5%
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 185,000 reported delay minutes here, that single category outweighs weather by 8 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.

33% 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 61,000 minutes out of 185,000, against a national NAS share of 21%.

Cancellations run at 2.59%, against 1.80% nationally. That is about 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. 14.3% 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 72.4% on time across 7,556 flights, 5 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 5 points of difference.

The sample behind these figures is 7,561 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. May runs 76.6% on time and September 56.2%, a swing of 20 points. If the dates move at all, move them out of September before you think about anything else.

Common questions

ORD to BOS questions

How often is ORD to BOS delayed?

About one flight in three arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 32.3% of the 7,561 flights in this analysis, against 22.6% nationally. Delayed flights are late by a little over an hour on average.

Which airline is most reliable on ORD to BOS?

Envoy Air leads at 82.6% on time across 449 flights. American Airlines is at the other end on 60.7%, a gap of 22 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 ORD to BOS?

The 5am–8am departure window is the strongest at 86.3% on time. The 2pm–5pm window is the weakest at 54.6%, 32 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 September delays on ORD to BOS?

September is the weakest month at 56.2% on time, compared with 76.6% in May. Across the year that is 20 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. ORD to BOS and BOS to ORD 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