Carrier route record
DLBOI→SLC
Delta Air Lines · Boise to Salt Lake City
- Flights
- 1,219
- Period
- September 2025 to August 2026
- Share of route
- 70%
- Carriers
- 2
Historical statistics for September 2025 to August 2026, not live status. For today’s flights, check with Delta Air Lines.
Delta on BOI to SLC earns an A. Close to nine flights in ten arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 12 points better than the national rate of 77.3%. When something does go wrong the average delay runs an hour and a half. That rests on 1,219 flights, with a median arrival 11 minutes early.
Set against the rest of the country, Delta's BOI to SLC record is 12 points better than the US average of 77.3%. That gap is worth roughly 121 fewer late arrivals for every thousand flights.
Key figures
On time
89.4%
Arrivals under 15 minutes late, of 1,202 completed flights
Avg delay
87 min
Across delayed arrivals only, not all flights
Cancelled
1.31%
National rate is 1.89%
Whole route
91.1%
Every carrier on BOI to SLC, 1,732 flights
These figures cover 1,219 flights between September 2025 and August 2026. The median arrival is 11 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 BOI to SLC
Delta flew 1,219 of the 1,732 flights on BOI to SLC, most of the route. Its 89.4% on time is 2 points worse than the route as a whole, which runs 91.1%. Ranked by on-time rate it is last of two carriers on the route, where the range runs from SkyWest at 94.9% to Delta at 89.4%.
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 |
|---|---|---|---|---|---|
| SkyWest Airlines | 513 | 94.9% | 69 min | 0.19% | A+ |
| Delta Air Lines (this page) | 1,219 | 89.4% | 87 min | 1.31% | A |
Flight by flight
Delta flight numbers on BOI to SLC
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Departure window
When Delta runs best on this route
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 1,219 flights.
- 5am–8am354 flights90.2%
- 8am–11am164 flights93.9%
- 11am–2pm544 flights89.2%
- 2pm–5pm—
- 5pm–8pm157 flights84.0%
- 8pm–5am—
Scale runs 75% to 100%. Rows with fewer than 30 flights show a dash.
Book the morning departure. Flights leaving between 8am–11am arrive on time 93.9% of the time, against 84.0% for the evening window. That is 10 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 11am–2pm window is the busiest, with 544 flights scheduled in it.
Across the year
Delta on BOI to SLC through the year
January is the weak month at 83.5% on time, against 95.7% in May. 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. August was the busiest month here, with 122 flights.
Across the week, Friday is the strongest day at 92.0% on time and Thursday the weakest at 86.3%, a spread of 6 points.
Arrival by arrival
How late Delta on BOI to SLC runs when it is late
Delta on BOI to SLC often beats the schedule: 454 of 1,202 completed flights, 38%, arrived 15 minutes or more early. The 127 late arrivals split 49 under half an hour, 33 between 30 and 60 minutes, and 45 an hour or more.
- 15+ min early454 flights37.8%
- Within 15 min621 flights51.7%
- 15–29 min late49 flights4.1%
- 30–59 min late33 flights2.7%
- 1–2 hours late23 flights1.9%
- 2+ hours late22 flights1.8%
Scale runs 0% to 100%.
Share of 1,202 completed flights by arrival against schedule.
20 of 117 late departures made up the time and arrived on time, 17% of them. 30 flights left on time and still arrived late.
The worst days
Worst days for Delta on BOI to SLC
The latest arrival of the period was on 27 October 2025, 12 hours 1 minute behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on five of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 27 October 2025 | 12 hours 1 minute | Carrier |
| 18 February 2026 | 9 hours 36 minutes | Carrier |
| 2 April 2026 | 8 hours 33 minutes | Carrier |
| 13 November 2025 | 8 hours 8 minutes | Carrier |
| 18 June 2026 | 6 hours 58 minutes | Carrier |
Delay causes
Why Delta runs late on this route
Carrier accounts for 54% of the 11,000 delay minutes carriers reported here, and the remaining four split what is left.
- 54%Carrier
- 32%Late-arriving aircraft
- 11%National Airspace System
- 3%Extreme weather
The largest share of delay minutes, 54%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 5,962 of the 11,000 delay minutes reported here. The split is drawn from 11,015 reported delay minutes.
The practical consequence: the 8am–11am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 93.9% on time here.
Cancellations sit at 1.31% against a national 1.89%, which is ordinary. Diversions add another 0.08%.
Connections and stage length
What a delay here costs
Badly late arrivals are rare here: only 3.7% land an hour or more behind schedule, against 8.3% nationally. Connections built on this flight are about as safe as US domestic connections get, though a cancelled flight still ignores every layover you give it.
At 290 miles this is a short hop, and stage length matters more than it looks. A flight this short spends under two hours in the air, which leaves almost nothing to claw back a late pushback with. Delay here is decided on the ground, in the turn, which is why the 8am–11am window matters as much as it does.
The return leg is a different operation and performs like one: it runs 84.0% on time across 1,219 flights, 5 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 5 points of difference.
The sample behind these figures is 1,219 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.
What to do with this
Booking Delta on BOI to SLC
Put together: the calendar is the biggest lever here, not the carrier or the hour. May runs 95.7% on time and January 83.5%, a swing of 12 points. If the dates move at all, move them out of January before you think about anything else. 1,202 completed flights over 12 months sit behind that.
Related
Where to go next
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.