Route reliability record
BOS→DEN
Boston to Denver
- Flights
- 3,847
- Period
- September 2025 to August 2026
- Distance
- 1,754 mi
- Carriers
- 4
This route 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 77.3%. The late ones land about an hour behind schedule. That rests on 3,847 BOS to DEN flights, of which Delta Air Lines flew 365 at 83.6% on time.
Best time to fly BOS to DEN: a 5am–8am departure, ideally on a Wednesday. Flights in that window arrived on time 87.5% of the time and Wednesday flights 79.0%, against 75.7% for the route overall.
Delta Air Lines is the most reliable of the four carriers covered here at 83.6% on time across 365 flights.
Key figures
On time
75.7%
Arrivals under 15 minutes late, of 3,778 completed flights
Avg delay
62 min
Across delayed arrivals only, not all flights
Cancelled
1.38%
National rate is 1.89%
Best carrier
Delta
83.6% on time across 365 flights
These figures cover 3,847 flights between September 2025 and August 2026. Beyond the headline rate, 8.1% of arrivals land a full hour or more behind schedule, against 8.3% nationally.
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Carrier by carrier
Which airline is most reliable on BOS to DEN
The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 83.6% of the time; Southwest Airlines manages 63.9%. Sample sizes sit next to every figure, because a two-point gap across 908 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Delta Air Lines | 365 | 83.6% | 53 min | 1.37% | B |
| United Airlines | 1,884 | 82.5% | 70 min | 1.11% | B |
| JetBlue Airways | 690 | 68.4% | 63 min | 2.61% | C |
| Southwest Airlines | 908 | 63.9% | 55 min | 0.99% | D+ |
The spread between Delta and Southwest is 20 points, wide enough that it should decide the booking. On a hundred trips that is 20 more arrivals inside the on-time window.
Flight by flight
Flights on BOS to DEN
The flight numbers below flew this route at least 250 times in the period, busiest first. Each has its own record, with its schedule and delay causes.
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Best ways to make this trip
The most reliable ways to fly Boston to Denver
Every airline on this route, ranked by how often a scheduled flight actually operated and arrived on time, with its best departure time and most punctual flight number. No nearby airport pair beat these.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. BOS → DENBoston to Denver | Delta Air Lines | 82.5% | 83.6% | 1.37% | 5am–8am, Sat | DL 499 07:45 |
| 2. BOS → DENBoston to Denver | United Airlines | 81.6% | 82.5% | 1.11% | 5am–8am, Wed | UA 647 07:45 |
| 3. BOS → DENBoston to Denver | JetBlue Airways | 66.6% | 68.4% | 2.61% | 5am–8am, Wed | B6 993 19:59 |
| 4. BOS → DENBoston to Denver | Southwest Airlines | 63.3% | 63.9% | 0.99% | 5am–8am, Tue | — |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
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 37 points, against 20 points between the best and worst carrier.
- 5am–8am1,138 flights87.5%
- 8am–11am520 flights82.8%
- 11am–2pm620 flights79.7%
- 2pm–5pm714 flights75.4%
- 5pm–8pm587 flights50.8%
- 8pm–5am268 flights57.6%
Scale runs 40% to 95%.
The 5pm–8pm window is where this operation falls apart: 50.8% on time, against 87.5% 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 1,138 flights scheduled in it.
Explore
Filter BOS to DEN by airline, time, month and day
Pick a breakdown and a carrier. The dashed mark on each row is the same slice for every US flight.
On BOS to DEN, the best departure window is 5am–8am at 87.5% on time and the worst is 5pm–8pm at 50.8%, a wide gap of 36.7 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am87.5%
- 8–11am82.8%
- 11am–2pm79.7%
- 2–5pm75.4%
- 5–8pm50.8%
- 8pm–5am57.6%
best all US flightsScale 40% to 95%.
Across the year
When delays peak on this route
This route's year swings by 23 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.
August is the worst month at 65.1% on time, 23 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 396 flights.
Across the week, Wednesday is the strongest day at 79.0% on time and Sunday the weakest at 72.3%, a spread of 7 points.
Delay causes
Why this route gets delayed
Late-arriving aircraft accounts for 44% of the 57,000 delay minutes carriers reported here, and the remaining four split what is left.
- 44%Late-arriving aircraft
- 27%Carrier
- 27%National Airspace System
- 2%Extreme weather
- 0%Security
44% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 57,000 reported delay minutes here, that single category outweighs weather by 23 to one. The split is drawn from 57,071 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 87.5% on time here.
Cancellations sit at 1.38% against a national 1.89%, which is ordinary. Diversions add another 0.42%.
Connections and stage length
What a delay here actually costs
8.1% of arrivals land an hour or more late, close to the national 8.3%, so 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 69.6% on time across 3,851 flights, 6 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 6 points of difference.
The sample behind these figures is 3,847 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.
Work out the risk of missing a connection in DEN after this flight
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 August 65.1%, a swing of 23 points. If the dates move at all, move them out of August before you think about anything else. 3,778 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 arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 24.3% of the 3,847 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on BOS to DEN?
Delta Air Lines leads at 83.6% on time across 365 flights. Southwest Airlines is at the other end on 63.9%, a gap of 20 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 87.5% on time. The 5pm–8pm window is the weakest at 50.8%, 37 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 August delays on BOS to DEN?
August is the weakest month at 65.1% on time, compared with 87.7% in November. Across the year that is 23 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.
Related
Where to go next
- DEN to BOS — the return legseparate record
- Boston Logan International (BOS) delay statistics
- Denver International (DEN) delay statistics
- Delta Air Lines on BOS to DEN83.6%
- United Airlines on BOS to DEN82.5%
- JetBlue Airways on BOS to DEN68.4%
- Southwest Airlines on BOS to DEN63.9%
- BOS to DCA, a related route72.6%
- PHX to DEN, a related route76.7%
- BOS to ORD, a related route71.9%
- Delta Air Lines on-time record83.6%
- United Airlines on-time record82.5%
- JetBlue Airways on-time record68.4%
- Why the first flight of the morning is statistically safest
- Same route, different airline: where the carrier you pick matters most
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.
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Source: US DOT Bureau of Transportation Statistics, on-time performance data, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.