Carrier route record
DLBOS→SLC
Delta Air Lines · Boston to Salt Lake City
- Flights
- 1,083
- Period
- July 2025 to June 2026
- Share of route
- 86%
- Carriers
- 2
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Delta Air Lines.
Delta on BOS to SLC lands a B, level with the national rate of 77.6%. Roughly one flight in five arrives 15 minutes late or worse, and those flights are late by a little over an hour on average. That is a workable record, not a spotless one. That rests on 1,083 flights, with a median arrival 4 minutes early.
The US average over the same twelve months is 77.6%, so there is little to separate Delta on BOS to SLC from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.
Key figures
On time
77.8%
Arrivals under 15 minutes late, of 1,067 completed flights
Avg delay
68 min
Across delayed arrivals only, not all flights
Cancelled
1.20%
National rate is 1.81%
Whole route
75.4%
Every carrier on BOS to SLC, 1,256 flights
These figures cover 1,083 flights between July 2025 and June 2026. The median arrival is 4 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 BOS to SLC
Delta flew 1,083 of the 1,256 flights on BOS to SLC, most of the route. Its 77.8% on time is 2 points better than the route as a whole, which runs 75.4%. Ranked by on-time rate it is first of two carriers on the route, where the range runs from Delta at 77.8% to JetBlue at 59.9%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.
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 (this page) | 1,083 | 77.8% | 68 min | 1.20% | B |
| JetBlue Airwaysthin sample | 173 | 59.9% | 53 min | 3.47% | D− |
Flight by flight
Delta flight numbers on BOS to SLC
Departure window
When Delta runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 20 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am365 flights87.7%
- 8am–11am306 flights77.1%
- 11am–2pm50 flights68.0%
- 2pm–5pm24 flights—
- 5pm–8pm338 flights68.6%
- 8pm–5am—
Scale runs 60% to 95%. 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 68.0% on time against 87.7% for 5am–8am. 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 5am–8am window is the busiest, with 365 flights scheduled in it.
Across the year
Delta on BOS to SLC through the year
December is the weak month at 65.9% on time, against 87.8% in September. Winter delays cluster: a single storm system can account for most of a month's shortfall, so an average December hides both very good weeks and genuinely unflyable days. March was the busiest month here, with 95 flights.
Across the week, Monday is the strongest day at 85.3% on time and Sunday the weakest at 70.6%. 15 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. Carrier accounts for 49% of the 16,000 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.
- 49%Carrier
- 26%Late-arriving aircraft
- 25%National Airspace System
- 1%Extreme weather
The largest share of delay minutes, 49%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 7,825 of the 16,000 delay minutes reported here. The split is drawn from 16,124 reported delay minutes.
Cancellations sit at 1.20% against a national 1.81%, which is ordinary. Diversions add another 0.28%.
Connections and stage length
What a delay here costs
6.5% 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 a little over 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 83.3% on time across 1,083 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. 1,083 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 BOS to SLC
Put together: treat all of this as provisional. 1,083 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 77.8% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 1,067 completed flights over 12 months sit behind that.
Related
Where to go next
- BOS to SLC, every carrier
- Delta on SLC to BOS, the return leg
- JetBlue Airways on BOS to SLC59.9%
- Delta Air Lines network-wide record
- Boston Logan International (BOS) delay statistics
- Salt Lake City International (SLC) delay statistics
- The best time of day to fly, according to 7.04 million flight records
- Worst months to fly in the US, ranked by the data
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.