Carrier route record
DLBOS→SLC
Delta Air Lines · Boston to Salt Lake City
- Flights
- 1,083
- Period
- September 2025 to August 2026
- Share of route
- 86%
- Carriers
- 2
Historical statistics for September 2025 to August 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 77.3%. Roughly one flight in four arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 1,083 flights, with a median arrival 3 minutes early.
The US average over the same twelve months is 77.3%, 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
77.5%
Arrivals under 15 minutes late, of 1,069 completed flights
Avg delay
67 min
Across delayed arrivals only, not all flights
Cancelled
1.20%
National rate is 1.89%
Whole route
73.4%
Every carrier on BOS to SLC, 1,264 flights
These figures cover 1,083 flights between September 2025 and August 2026. The median arrival is 3 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
Delta against every carrier on BOS to SLC
Delta flew 1,083 of the 1,264 flights on BOS to SLC, most of the route. Its 77.5% on time is 4 points better than the route as a whole, which runs 73.4%. Ranked by on-time rate it is first of two carriers on the route, where the range runs from Delta at 77.5% to JetBlue at 48.0%. 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 | 77.5% | 67 min | 1.20% | B |
| JetBlue Airwaysthin sample | 181 | 48.0% | 58 min | 5.52% | F− |
Flight by flight
Delta flight numbers on BOS to SLC
Timetable by Aviasales, a Travelpayouts partner. Booking through it may earn this site a commission at no cost to you; it changes no figure here.
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 19 points, against half a point between the best and worst carrier.
- 5am–8am365 flights87.2%
- 8am–11am244 flights77.1%
- 11am–2pm112 flights70.5%
- 2pm–5pm32 flights84.4%
- 5pm–8pm330 flights68.7%
- 8pm–5am—
Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.
Book the early departure. Flights leaving between 5am–8am arrive on time 87.2% of the time, against 68.7% for the evening window. That is 19 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. 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 85.6% on time and Sunday the weakest at 67.5%, a spread of 18 points.
Arrival by arrival
How late Delta on BOS to SLC runs when it is late
The 241 late arrivals split 99 under half an hour, 73 between 30 and 60 minutes, and 69 an hour or more.
- 15+ min early243 flights22.7%
- Within 15 min585 flights54.7%
- 15–29 min late99 flights9.3%
- 30–59 min late73 flights6.8%
- 1–2 hours late37 flights3.5%
- 2+ hours late32 flights3.0%
Scale runs 0% to 100%.
Share of 1,069 completed flights by arrival against schedule.
36 of 173 late departures made up the time and arrived on time, 21% of them. In the other direction, 104 flights left on time yet arrived 15 minutes late or more, so that delay built up after pushback: in the air, in a holding pattern or on the ground at SLC.
The worst days
Worst days for Delta on BOS to SLC
The latest arrival of the period was on 27 January 2026, 17 hours 6 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on four of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 27 January 2026 | 17 hours 6 minutes | Carrier |
| 6 February 2026 | 9 hours 36 minutes | Carrier |
| 18 September 2025 | 9 hours 5 minutes | Late-arriving aircraft |
| 7 February 2026 | 6 hours 40 minutes | Carrier |
| 19 January 2026 | 6 hours 30 minutes | Carrier |
Delay causes
Why Delta runs late on this route
Carrier accounts for 48% of the 16,000 delay minutes carriers reported here, and the remaining four split what is left.
- 48%Carrier
- 26%Late-arriving aircraft
- 25%National Airspace System
- 1%Extreme weather
The largest share of delay minutes, 48%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 7,854 of the 16,000 delay minutes reported here. The split is drawn from 16,231 reported delay minutes.
Cancellations sit at 1.20% against a national 1.89%, which is ordinary. Diversions add another 0.09%.
Connections and stage length
What a delay here costs
6.5% 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 82.7% on time across 1,083 flights, 5 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 5 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 77.5% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 1,069 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 SLC48.0%
- 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 7.05 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, September 2025 to August 2026. Last updated ; recomputed monthly. How this data is collected.