Carrier route record

DLDEN→BOS

Delta Air Lines · Denver to Boston

Flights: 400
Period: July 2025 to June 2026
Share of route: 10%
Carriers: 4

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Delta Air Lines.

Delta on DEN to BOS sits in the middle of the pack with a B. Close to three flights in four arrive on time by the DOT's definition, 2 points worse than the national rate of 77.6%. The late ones land about an hour behind schedule. That rests on 400 flights. The strongest carrier on the route with a full sample, United Airlines, flew 1,911 at 77.1% on time.

United Airlines is the most reliable of the three carriers covered here at 77.1% on time across 1,911 flights.

On time

75.8%

Arrivals under 15 minutes late, of 393 completed flights

Avg delay

56 min

Across delayed arrivals only, not all flights

Cancelled

1.50%

National rate is 1.81%

Whole route

71.4%

Every carrier on DEN to BOS, 3,903 flights

These figures cover 400 flights between July 2025 and June 2026. The median arrival is 3 minutes early, which is the part an average hides: most flights here are fine, and the on-time rate is decided by a tail of badly late ones. On-time means under 15 minutes late, the DOT's own threshold.

Carrier by carrier

Delta against every carrier on DEN to BOS

Delta flew 400 of the 3,903 flights on DEN to BOS, about 10% of it. Its 75.8% on time is 4 points better than the route as a whole, which runs 71.4%. Ranked by on-time rate it is number two of four carriers on the route, where the range runs from United at 77.1% to Southwest at 59.7%.

The choice of carrier is not cosmetic here. United Airlines arrives on time 77.1% of the time; Southwest Airlines manages 59.7%. Sample sizes sit next to every figure, because a two-point gap across 910 flights means less than a ten-point one.

On-time performance by carrier on DEN to BOS
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	1,911	77.1%	70 min	0.84%	B+
Delta Air Lines (this page)	400	75.8%	56 min	1.50%	B
JetBlue Airways	682	68.6%	82 min	2.05%	C
Southwest Airlines	910	59.7%	66 min	1.10%	D

The spread between United and Southwest is 17 points, wide enough that it should decide the booking. On a hundred trips that is 17 more arrivals inside the on-time window.

Flight by flight

Delta flight numbers on DEN to BOS

DL 49911:3075.2% · 349 flights

Departure window

When Delta runs best on this route

Departure time is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 400 flights.

5am–8am—
8am–11am—
11am–2pm365 flights75.2%
2pm–5pm—
5pm–8pm—
8pm–5am35 flights82.4%

Scale runs 65% to 90%. Rows with fewer than 30 flights show a dash.

The weak window here is the middle of the day, not the evening: 11am–2pm runs 75.2% on time against 82.4% for 8pm–5am. That shape usually means a departure bank rather than an accumulating delay, so the recovery later in the afternoon is real rather than noise. The 11am–2pm window is the busiest, with 365 flights scheduled in it.

Across the year

Delta on DEN to BOS through the year

Darker means more delays. Figures are on-time percentages.March best, September worst

Delays peak in September, when the on-time rate falls to 40.0%. March is the strongest month at 90.3%. Moving a flexible trip across that boundary buys 50 points. July was the busiest month here, with 59 flights.

Across the week, Saturday is the strongest day at 90.9% on time and Tuesday the weakest at 66.7%. 24 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Delta runs late on this route

One category carries most of the weight here. National Airspace System accounts for 68% of the 5,324 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.

National Airspace System
68%
Late-arriving aircraft
21%
Carrier
9%
Extreme weather
2%

68% 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 3,615 minutes out of 5,324, against a national NAS share of 21%. The split is drawn from 5,324 reported delay minutes.

Cancellations sit at 1.50% against a national 1.81%, which is ordinary. Diversions add another 0.25%.

Connections and stage length

What a delay here costs

7.9% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last about an hour, which a normal layover absorbs.

At 1,754 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.

The return leg is a different operation and performs like one: it runs 81.4% on time across 400 flights, 6 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 6 points of difference.

One caution: this is a thin sample. 400 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 DEN to BOS

Put together: treat all of this as provisional. 400 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 75.8% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 393 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