Route profile
SEA→BOS
Flight reliability, delays and best times to fly from Seattle to Boston, 2,496 miles.
Right now
Aviation weather is not currently a factor.
Aviation weather is not currently a factor.
Route reliability
July 2023 – July 2026
Better than 44% of comparable major US routes (4,598 compared)
Calculated from 7,902 flights. How this is calculated
SEA → BOS arrives on time 75.2% of the time; the return trip, BOS → SEA, arrives on time 75.7% of the time.
SEA → BOS spends 32.5 minutes on the ground on a 2,496-mile trip: 21.8 minutes from pushback to wheels-up at SEA and 10.7 minutes from touchdown to gate at BOS.
Source: US DOT Bureau of Transportation Statistics · Data covering July 2023 – July 2026
What stands out
The airline matters unusually much on this route, a wider carrier-to-carrier gap than 97% of 2,692 comparable routes.
Delta Air Lines arrived on time 83.9% of the time, against 60.7% for JetBlue, flying the exact same route.
Source: FlyerIntel analysis of US DOT BTS data · July 2023 – July 2026 · Ranked against every other route with the same kind of figure and at least 2,692 in the comparison.
What sets this route apart
Where SEA to BOS differs most from similar routes by hour, weekday, month and airline, July 2023 – July 2026.
SEA to BOS struggles most at 11 AM: 54.0% of its flights scheduled then arrive on time, 24 points behind the 78.0% on routes of similar length at the same hour. Against all other routes the gap is 27 points.
Thursday is the day SEA to BOS slips furthest against routes of similar length, 71.9% on time where they average 77.1%, 5.2 points lower. Against all other routes the gap is 4.9 points.
In September, SEA to BOS runs 11.2 points below routes of similar length, 70.7% on time to 81.9%. Against all other routes the gap is 11.7 points.
March is kinder to SEA to BOS than to routes of similar length: 83.4% on time against 79.0%, 4.4 points better. Against all other routes the gap is 5.5 points.
JetBlue’s flights on SEA to BOS arrive on time 60.7% of the time, 14.8 points below the 75.5% it manages on its routes of similar length. Against all other routes the gap is 11.5 points.
SEA to BOS against comparable routes
July 2023 – July 2026| Measure | This route | Compared with | Them | Gap | Flights behind it |
|---|---|---|---|---|---|
| Hour: 11 AM departures | 54.0% | routes of similar length | 78.0% | −24.0 pts | 428 here, 46,476 there |
| Weekday: Thursday | 71.9% | routes of similar length | 77.1% | −5.2 pts | 1,158 here, 144,071 there |
| Month: September | 70.7% | routes of similar length | 81.9% | −11.2 pts | 686 here, 78,951 there |
| Month: March | 83.4% | routes of similar length | 79.0% | +4.4 pts | 549 here, 77,445 there |
| Airline: JetBlue | 60.7% | routes of similar length | 75.5% | −14.8 pts | 1,187 here, 116,573 there |
Each comparison pools the flights of other routes, with this route’s own left out. Similar length means within 15% of this route’s 2,496 miles, with at least 5 such routes. A bucket is set against the most comparable group that has enough flights: similar length, then the same origin (at least 3 routes), then all other routes. Hours, weekdays and months appear only where both sides have 120 completed flights, and airlines where both have 600. The gap must be at least 2 points and 2 standard errors, and only the largest gap each way is kept per measure. These are differences in the flights counted, not causes.
Why SEA → BOS flights are cancelled
July 2023 – July 2026
SEA → BOS cancelled 74 of 7,902 scheduled flights — about 1 in every 107. The reason filed most often was the airline, 63.5% of the cancellations coded on this route — about 1 in every 168 scheduled flights.
Share of cancellations
Of 74 cancelled departures carrying a reason code.
What each reason means
Crew, maintenance, aircraft cleaning, baggage or fueling: what BTS counts as within the carrier’s own control.
47 cancellations, 63.5% of the total.
Conditions the carrier judged severe enough to stop the flight: a blizzard, a hurricane, a line of thunderstorms.
22 cancellations, 29.7% of the total.
Airport capacity, air traffic control flow programs, heavy traffic and ordinary bad weather. A system decision, not the airline’s.
5 cancellations, 6.8% of the total.
A terminal evacuation, a security breach, screening equipment failure, or screening queues over 29 minutes.
0 cancellations, 0.0% of the total.
Reason codes are the operating airline’s own filing with US DOT, not an independent finding of fault. Ordinary bad weather is filed under air traffic, so weather’s full share is larger than its bar.
74 coded cancellations were recorded on SEA → BOS; the section appears from 50.
When it goes wrong
July 2023 – July 2026
46 min late
against a median of 4 min early
Percentiles over 7,902 operations; cancelled and diverted flights are counted separately.
Will your connection be tight enough?
Layovers at BOS after arriving from SEA.
| Connection time | Chance of missing | Reads as |
|---|---|---|
| 30 min | 42% | Likely to miss |
| 45 min | 24% | High risk |
| 60 min | 14% | Some risk |
| 90 min | 7.4% | Some risk |
| 120 min | 4.3% | Low risk |
This is one leg of a connection. Gate changes and the next flight's own schedule matter too. And a connection can fail before delay is even the question — this route cancels 0.94% of the time and diverts 0.28% of the time, which a late arrival never shows up in.
Chance of missing is the share of 7,806 arrivals on this route that landed later than the connection time less 30 minutes to reach the next gate.
The worst tenth of arrivals on this route land at least 46 minutes late (90th-percentile gate arrival delay), over 7,902 operations.
Any other layover length: connection checker.
Best time to fly
SEA → BOS flights departing 5–9 AM arrived on time 84.9% of the time, against 50.0% for 12–3 PM departures, a gap of 34.9 percentage points.
By departure window
By departure hour
- 12 AM to 5 AM: too few flights to score
- 6 AM: 88.9% on time from 270 flights
- 7 AM: 88.2% on time from 1,356 flights
- 8 AM: 71.9% on time from 428 flights
- 9 AM: 69.9% on time from 254 flights
- 10 AM: 55.9% on time from 556 flights
- 11 AM: 54.0% on time from 434 flights
- 12 PM to 2 PM: too few flights to score
- 3 PM: 75.8% on time from 1,691 flights
- 4 PM to 8 PM: too few flights to score
- 9 PM: 70.0% on time from 770 flights
- 10 PM: 80.1% on time from 721 flights
- 11 PM: 79.0% on time from 1,107 flights
Departure windows with fewer than 120 flights are not scored.
Why SEA → BOS runs late
July 2023 – July 2026
crew, maintenance, boarding and fueling, all within the carrier’s control
airspace and airport capacity, including weather-driven flow control
the inbound aircraft was late, so this flight started late
weather severe enough to stop this flight specifically
screening or terminal security incidents
Share of the delay minutes US DOT attributed to each cause for SEA → BOS. Only delays of 15 minutes or more are attributed.
Airlines on this route
Carriers with at least 200 flights, by the airline that operated each one.
| Carrier | Flights | On time | Cancelled | Median delay | Severe |
|---|---|---|---|---|---|
| Alaska Airlines | 3,714 | 72.9% | 0.75% | -2 min | 6.8% |
| Delta Air Lines | 2,980 | 83.9% | 1.07% | -9 min | 4.5% |
| JetBlue | 1,208 | 60.7% | 1.16% | 5 min | 17.5% |
Alaska Airlines flew 47.0% of the 7,902 flights listed.
Delta Air Lines arrived on time 23.2 percentage points more often than JetBlue on this route.
Flights on this route
Flight numbers with at least 600 operations here and still on the schedule.
DL459 (7:50 AM) arrived on time 89.4% of the time, 16.7 points more often than AS536 (9:25 PM) at 72.7%.
Weekly and seasonal patterns
By day of week
Wednesday is historically the most reliable day and Thursday the least, a gap of 6.4 percentage points.
By month
- Jan: 79.6%
- Feb: 80.3%
- Mar: 83.4%
- Apr: 77.6%
- May: 73.2%
- Jun: 72.7%
- Jul: 67.4%
- Aug: 69.0%
- Sep: 70.7%
- Oct: 79.8%
- Nov: 84.5%
- Dec: 78.3%
July is historically the weakest month and November the strongest, a spread of 17.1 percentage points.
Reliability over time
July 2023 – July 2026
- July 2023: 71.0% from 268 flights
- August 2023: 77.8% from 271 flights
- September 2023: 70.0% from 225 flights
- October 2023: 82.5% from 229 flights
- November 2023: 83.3% from 203 flights
- December 2023: 77.6% from 184 flights
- January 2024: 70.7% from 157 flights
- February 2024: 78.6% from 154 flights
- March 2024: 80.4% from 189 flights
- April 2024: 69.0% from 210 flights
- May 2024: 73.2% from 238 flights
- June 2024: 77.2% from 252 flights
- July 2024: 73.3% from 271 flights
- August 2024: 64.2% from 273 flights
- September 2024: 74.8% from 234 flights
- October 2024: 84.3% from 230 flights
- November 2024: 87.2% from 187 flights
- December 2024: 72.3% from 185 flights
- January 2025: 83.2% from 150 flights
- February 2025: 82.3% from 146 flights
- March 2025: 83.6% from 191 flights
- April 2025: 88.2% from 196 flights
- May 2025: 62.4% from 228 flights
- June 2025: 70.4% from 255 flights
- July 2025: 59.5% from 274 flights
- August 2025: 64.9% from 270 flights
- September 2025: 67.2% from 229 flights
- October 2025: 72.4% from 227 flights
- November 2025: 82.8% from 164 flights
- December 2025: 86.2% from 161 flights
- January 2026: 86.0% from 129 flights
- February 2026: 80.3% from 129 flights
- March 2026: 86.5% from 172 flights
- April 2026: 76.0% from 172 flights
- May 2026: 83.0% from 254 flights
- June 2026: 70.8% from 278 flights
- July 2026: 66.1% from 317 flights
Over the most recent 12 months (2025-08 to 2026-07), on-time arrivals averaged 75.1% against 74.7% in the 12 months before — broadly unchanged.
Data and methodology
Calculated by FlyerIntel from 7,902 SEA → BOS flight records from the US DOT Bureau of Transportation Statistics, covering July 2023 – July 2026. Late means 15 or more minutes past scheduled arrival; cancelled and diverted flights are left out of on-time rates.
Full methodology · Data sources · Report a problem
Related research: How Long a Layover Needs to Be · Two Airlines on One Route · Best Time of Day to Fly From Major US Airports
Analysis last recomputed