Carrier route record
DLSLC→BOI
Delta Air Lines · Salt Lake City to Boise
- 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 SLC to BOI earns a B. More than four flights in five arrive inside the 15-minute window the DOT uses to define an on-time arrival, which puts it 7 points better than the national rate of 77.3%. When something does go wrong the average delay runs about an hour. That rests on 1,219 flights, with a median arrival 9 minutes early.
Set against the rest of the country, Delta's SLC to BOI record is 7 points better than the US average of 77.3%. That gap is worth roughly 67 fewer late arrivals for every thousand flights.
Key figures
On time
84.0%
Arrivals under 15 minutes late, of 1,206 completed flights
Avg delay
61 min
Across delayed arrivals only, not all flights
Cancelled
1.07%
National rate is 1.89%
Whole route
86.3%
Every carrier on SLC to BOI, 1,732 flights
These figures cover 1,219 flights between September 2025 and August 2026. The median arrival is 9 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 SLC to BOI
Delta flew 1,219 of the 1,732 flights on SLC to BOI, most of the route. Its 84.0% on time is 2 points worse than the route as a whole, which runs 86.3%. Ranked by on-time rate it is last of two carriers on the route, where the range runs from SkyWest at 91.8% to Delta at 84.0%.
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 | 91.8% | 54 min | 0.19% | A+ |
| Delta Air Lines (this page) | 1,219 | 84.0% | 61 min | 1.07% | B |
Flight by flight
Delta flight numbers on SLC to BOI
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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–8am—
- 8am–11am507 flights86.0%
- 11am–2pm135 flights88.1%
- 2pm–5pm157 flights84.1%
- 5pm–8pm14 flights—
- 8pm–5am406 flights80.0%
Scale runs 70% to 95%. Rows with fewer than 30 flights show a dash.
The best window here is not the first bank but the 11am–2pm slot at 88.1% on time, ahead of 8pm–5am at 80.0%. Where the curve peaks mid-day rather than at dawn, the constraint is usually congestion at one end rather than the aircraft's own rotation. The 8am–11am window is the busiest, with 507 flights scheduled in it.
Across the year
Delta on SLC to BOI through the year
December is the weak month at 76.2% on time, against 89.3% in June. 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, Tuesday is the strongest day at 89.8% on time and Sunday the weakest at 80.4%, a spread of 9 points.
Arrival by arrival
How late Delta on SLC to BOI runs when it is late
Delta on SLC to BOI often beats the schedule: 386 of 1,206 completed flights, 32%, arrived 15 minutes or more early. The 193 late arrivals split 81 under half an hour, 57 between 30 and 60 minutes, and 55 an hour or more.
- 15+ min early386 flights32.0%
- Within 15 min627 flights52.0%
- 15–29 min late81 flights6.7%
- 30–59 min late57 flights4.7%
- 1–2 hours late33 flights2.7%
- 2+ hours late22 flights1.8%
Scale runs 0% to 100%.
Share of 1,206 completed flights by arrival against schedule.
58 of 226 late departures made up the time and arrived on time, 26% of them. 25 flights left on time and still arrived late.
The worst days
Worst days for Delta on SLC to BOI
The latest arrival of the period was on 18 May 2026, 9 hours 58 minutes behind schedule; most of its delay minutes were filed as carrier-caused (crew, maintenance, fuelling, baggage). The same cause led on three of the five worst days.
| Date | Arrived late by | Largest filed cause |
|---|---|---|
| 18 May 2026 | 9 hours 58 minutes | Carrier |
| 21 July 2026 | 7 hours 55 minutes | Carrier |
| 9 August 2026 | 6 hours 16 minutes | Extreme weather |
| 26 September 2025 | 5 hours 52 minutes | Carrier |
| 7 June 2026 | 5 hours 24 minutes | Late-arriving aircraft |
Delay causes
Why Delta runs late on this route
Carrier accounts for 62% of the 12,000 delay minutes carriers reported here, and the remaining four split what is left.
- 62%Carrier
- 23%Late-arriving aircraft
- 8%Extreme weather
- 7%National Airspace System
The largest share of delay minutes, 62%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 7,237 of the 12,000 delay minutes reported here. The split is drawn from 11,676 reported delay minutes.
Cancellations sit at 1.07% against a national 1.89%, which is ordinary. Diversions add another 0.00%.
Connections and stage length
What a delay here costs
Badly late arrivals are rare here: only 4.6% 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 11am–2pm window matters as much as it does.
The return leg is a different operation and performs like one: it runs 89.4% on time across 1,219 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.
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 SLC to BOI
Put together: the calendar is the biggest lever here, not the carrier or the hour. June runs 89.3% on time and December 76.2%, a swing of 13 points. If the dates move at all, move them out of December before you think about anything else. 1,206 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.