Route reliability record
SLC→BOS
Salt Lake City to Boston
- Flights
- 1,264
- Period
- September 2025 to August 2026
- Distance
- 2,105 mi
- Carriers
- 2
This route lands a B, 3 points better than the national rate of 77.3%. About one flight in five arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 1,264 SLC to BOS flights, with a median arrival 8 minutes early.
Best time to fly SLC to BOS: a 8pm–5am departure, ideally on a Saturday. Flights in that window arrived on time 84.3% of the time and Saturday flights 86.3%, against 80.6% for the route overall.
The US average over the same twelve months is 77.3%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
80.6%
Arrivals under 15 minutes late, of 1,237 completed flights
Avg delay
62 min
Across delayed arrivals only, not all flights
Cancelled
1.98%
National rate is 1.89%
Best carrier
Delta
82.7% on time across 1,083 flights
These figures cover 1,264 flights between September 2025 and August 2026. The median arrival is 8 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.
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Carrier by carrier
Which airline is most reliable on SLC to BOS
Only one carrier clears this site's 365-flight floor here, so there is no comparison to draw. The table below is the full picture.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Delta Air Lines | 1,083 | 82.7% | 59 min | 1.29% | B |
| JetBlue Airwaysthin sample | 181 | 67.6% | 71 min | 6.08% | C− |
Flight by flight
Flights on SLC to BOS
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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Departure window
The best time of day to leave
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 1,264 flights.
- 5am–8am8 flights—
- 8am–11am374 flights81.1%
- 11am–2pm26 flights—
- 2pm–5pm—
- 5pm–8pm363 flights76.2%
- 8pm–5am493 flights84.3%
Scale runs 70% to 90%. Rows with fewer than 30 flights show a dash.
The overnight block holds up unusually well at 84.3% on time across 493 flights. Red-eyes fly into empty airspace and empty gates, and they are the first rotation of the aircraft's day rather than the last. The 8pm–5am window is the busiest, with 493 flights scheduled in it.
Explore
Filter SLC to BOS 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 SLC to BOS, the best departure window is 8pm–5am at 84.3% on time and the worst is 5pm–8pm at 76.2%, a real gap of 8.1 points. All US flights leaving 8pm–5am ran 70.1%.
- 5–8am—
- 8–11am81.1%
- 11am–2pm—
- 2–5pm—
- 5–8pm76.2%
- 8pm–5am84.3%
best all US flightsScale 60% to 95%. Cells under 30 flights show a dash.
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 69.9% on time, 23 points below May, the best at 92.4%. 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. March was the busiest month here, with 132 flights.
Across the week, Saturday is the strongest day at 86.3% on time and Monday the weakest at 77.7%, a spread of 9 points.
Delay causes
Why this route gets delayed
Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 15,000 reported delay minutes.
- 40%Late-arriving aircraft
- 31%National Airspace System
- 27%Carrier
- 2%Extreme weather
40% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 15,000 reported delay minutes here, that single category outweighs weather by 19 to one. The split is drawn from 14,820 reported delay minutes.
Cancellations sit at 1.98% against a national 1.89%, which is ordinary. Diversions add another 0.16%.
Connections and stage length
What a delay here actually costs
6.8% 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 2,105 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 73.4% on time across 1,264 flights, 7 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 7 points of difference.
The sample behind these figures is 1,264 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 BOS 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. May runs 92.4% on time and August 69.9%, a swing of 23 points. If the dates move at all, move them out of August before you think about anything else. 1,237 completed flights over 12 months sit behind that.
Common questions
SLC to BOS questions
How often is SLC to BOS delayed?
About one flight in five arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 19.4% of the 1,264 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
How reliable is SLC to BOS compared with the rest of the country?
80.6% of flights arrive on time here against a national 77.3%, a difference of 3 points in its favour. That is worth a B on this site's grading scale.
What time of day has the fewest delays on SLC to BOS?
The 8pm–5am departure window is the strongest at 84.3% on time. The 5pm–8pm window is the weakest at 76.2%, 8 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 SLC to BOS?
August is the weakest month at 69.9% on time, compared with 92.4% in May. 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
- BOS to SLC — the return legseparate record
- Salt Lake City International (SLC) delay statistics
- Boston Logan International (BOS) delay statistics
- Delta Air Lines on SLC to BOS82.7%
- JetBlue Airways on SLC to BOS67.6%
- SLC to DEN, a related route79.0%
- DCA to BOS, a related route70.1%
- SLC to PHX, a related route83.5%
- Delta Air Lines on-time record82.7%
- JetBlue Airways on-time record67.6%
- Why the first flight of the morning is statistically safest
- The best time of day to fly, according to 7.05 million flight records
Direction matters. SLC to BOS and BOS to SLC 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.