Route reliability record

ORD→PHL

Chicago to Philadelphia

Flights: 4,818
Period: June 2025 to May 2026
Distance: 678 mi
Carriers: 4

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, 7 points worse than the national rate of 77.4%. The late ones land an hour and a half behind schedule. That rests on 4,818 flights, of which United Airlines flew 1,718 at 71.9% on time.

The national on-time rate over the same period is 77.4%, so this route runs 7 points behind the country as a whole. Across a thousand flights that is about 68 extra late arrivals.

On time

70.6%

Arrivals under 15 minutes late, of 4,677 completed flights

Avg delay

93 min

Across delayed arrivals only, not all flights

Cancelled

2.76%

National rate is 1.80%

Best carrier

United

71.9% on time across 1,718 flights

These figures cover 4,818 flights between June 2025 and May 2026. Beyond the headline rate, 13.2% 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 PHL

The two carriers here are closely matched: about a point 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.

On-time performance by carrier on ORD to PHL
Airline	Flights	On time	Avg delay	Cancelled	Grade
Republic Airwaysthin sample	25	80.0%	46 min	0.00%	B+
United Airlines	1,718	71.9%	76 min	1.22%	C
American Airlines	2,892	70.5%	98 min	3.67%	C−
Frontier Airlinesthin sample	183	57.6%	138 min	3.28%	D−

American Airlines cancels 3.7% 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 26 points, against about a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am807 flights86.0%
8am–11am714 flights76.4%
11am–2pm811 flights74.5%
2pm–5pm954 flights63.7%
5pm–8pm906 flights60.3%
8pm–5am626 flights63.8%

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

The 5pm–8pm window is where this operation falls apart: 60.3% on time, against 86.0% 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 25 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, July worst

July is the worst month at 55.2% on time, 25 points below February, the best at 80.5%. Summer afternoon convection and peak-season schedules land on the same weeks every year, so this is a pattern you can book around rather than a run of bad luck.

Across the week, Tuesday is the strongest day at 75.9% on time and Monday the weakest at 64.3%. 12 points is a smaller lever than departure hour, but it is free.

Delay causes

Why this route gets delayed

One category carries most of the weight here. Late-arriving aircraft accounts for 47% of the 127,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.

Late-arriving aircraft
47%
Carrier
29%
National Airspace System
18%
Extreme weather
6%
Security
0%

47% 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 127,000 reported delay minutes here, that single category outweighs weather by 7 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 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 86.0% on time here.

Cancellations run at 2.76%, 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. 13.2% 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 678 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 runs 72.3% on time across 4,812 flights, within 2 points of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.

The sample behind these figures is 4,818 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 80.5% on time and July 55.2%, a swing of 25 points. If the dates move at all, move them out of July before you think about anything else.

Common questions

ORD to PHL questions

How often is ORD to PHL delayed?

Roughly 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 29.4% of the 4,818 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 ORD to PHL?

United Airlines leads at 71.9% on time across 1,718 flights. American Airlines is at the other end on 70.5%, a gap of about a point. 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 PHL?

The 5am–8am departure window is the strongest at 86.0% on time. The 5pm–8pm window is the weakest at 60.3%, 26 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 July delays on ORD to PHL?

July is the weakest month at 55.2% on time, compared with 80.5% in February. Across the year that is 25 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 PHL and PHL 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