Route reliability record

BOS→DEN

Boston to Denver

Flights: 3,899
Period: July 2025 to June 2026
Distance: 1,754 mi
Carriers: 4

This route lands a B, about a point worse than the national rate of 77.6%. About one flight in four arrive 15 minutes late or worse, and those flights are late by about an hour on average. That is a workable record, not a spotless one. That rests on 3,899 flights, of which United Airlines flew 1,908 at 83.0% on time.

United Airlines is the most reliable of the four carriers covered here at 83.0% on time across 1,908 flights.

On time

76.5%

Arrivals under 15 minutes late, of 3,840 completed flights

Avg delay

58 min

Across delayed arrivals only, not all flights

Cancelled

1.18%

National rate is 1.81%

Best carrier

United

83.0% on time across 1,908 flights

These figures cover 3,899 flights between July 2025 and June 2026. The median arrival is 6 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

Which airline is most reliable on BOS to DEN

The choice of carrier is not cosmetic here. United Airlines arrives on time 83.0% of the time; Southwest Airlines manages 64.8%. 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 BOS to DEN
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	1,908	83.0%	64 min	1.00%	B
Delta Air Lines	400	81.4%	46 min	1.75%	B
JetBlue Airways	681	70.9%	60 min	1.76%	C
Southwest Airlines	910	64.8%	54 min	0.88%	D+

The spread between United and Southwest is 18 points, wide enough that it should decide the booking. On a hundred trips that is 18 more arrivals inside the on-time window.

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

5am–8am1,135 flights88.2%
8am–11am548 flights86.6%
11am–2pm614 flights81.9%
2pm–5pm717 flights74.4%
5pm–8pm660 flights50.2%
8pm–5am225 flights61.7%

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 88.2% 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 5am–8am window is the busiest, with 1,135 flights scheduled in it.

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.November best, July worst

July is the worst month at 68.5% on time, 19 points below November, the best at 87.7%. 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. July was the busiest month here, with 427 flights.

Across the week, Monday is the strongest day at 79.6% on time and Thursday the weakest at 71.6%. 8 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 45% of the 52,000 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
45%
National Airspace System
28%
Carrier
25%
Extreme weather
3%

45% 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 52,000 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. The split is drawn from 52,325 reported delay minutes.

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 88.2% on time here.

Cancellations sit at 1.18% against a national 1.81%, which is ordinary. Diversions add another 0.33%.

Connections and stage length

What a delay here actually costs

7.4% 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 are the about an hour kind, 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 71.4% on time across 3,903 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 3,899 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. November runs 87.7% on time and July 68.5%, a swing of 19 points. If the dates move at all, move them out of July before you think about anything else. 3,840 completed flights over 12 months sit behind that.

Common questions

BOS to DEN questions

How often is BOS to DEN delayed?

About 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 23.5% of the 3,899 flights in this analysis, against 22.4% nationally. Delayed flights are late by about an hour on average.

Which airline is most reliable on BOS to DEN?

United Airlines leads at 83.0% on time across 1,908 flights. Southwest Airlines is at the other end on 64.8%, a gap of 18 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 DEN?

The 5am–8am departure window is the strongest at 88.2% 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 July delays on BOS to DEN?

July is the weakest month at 68.5% on time, compared with 87.7% in November. 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 DEN and DEN 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, July 2025 to June 2026. Updated monthly. How this data is collected.

Key figures