Route reliability record
SEA→SLC
Seattle to Salt Lake City
- Flights
- 4,098
- Period
- September 2025 to August 2026
- Distance
- 689 mi
- Carriers
- 4
This route lands a B+, 6 points better than the national rate of 77.3%. About one flight in six arrives 15 minutes late or worse, and those flights are late by about 50 minutes on average. That rests on 4,098 SEA to SLC flights, of which Delta Air Lines flew 2,232 at 86.8% on time.
Best time to fly SEA to SLC: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 94.0% of the time and Tuesday flights 86.3%, against 83.4% for the route overall.
Delta Air Lines is the most reliable of the three carriers covered here at 86.8% on time across 2,232 flights.
Key figures
On time
83.4%
Arrivals under 15 minutes late, of 4,063 completed flights
Avg delay
49 min
Across delayed arrivals only, not all flights
Cancelled
0.78%
National rate is 1.89%
Best carrier
Delta
86.8% on time across 2,232 flights
These figures cover 4,098 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 SEA to SLC
The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 86.8% of the time; Alaska Airlines manages 79.6%. Sample sizes sit next to every figure, because a two-point gap across 1,424 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Delta Air Lines | 2,232 | 86.8% | 59 min | 0.49% | A+ |
| SkyWest Airlines | 365 | 79.7% | 46 min | 0.00% | B+ |
| Alaska Airlines | 1,424 | 79.6% | 40 min | 1.26% | B |
| Frontier Airlinesthin sample | 77 | 73.0% | 53 min | 3.90% | C− |
Delta leads Alaska by 7 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
Flights on SEA to SLC
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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Best ways to make this trip
The most reliable ways to fly Seattle to Salt Lake City
Every airline on this route, ranked by how often a scheduled flight actually operated and arrived on time, with its best departure time and most punctual flight number. No nearby airport pair beat these.
| Option | Airline | Success | On time | Cancelled | Best departure | Most punctual flight |
|---|---|---|---|---|---|---|
| 1. SEA → SLCSeattle to Salt Lake City | Delta Air Lines | 86.4% | 86.8% | 0.49% | 5am–8am, Sat | DL 1128 05:30 |
| 2. SEA → SLCSeattle to Salt Lake City | SkyWest Airlines | 79.7% | 79.7% | 0.00% | 8pm–5am, Tue | OO 3298 19:07 |
| 3. SEA → SLCSeattle to Salt Lake City | Alaska Airlines | 78.6% | 79.6% | 1.26% | 5am–8am, Wed | AS 733 11:51 |
Success is the share of scheduled flights that operated and arrived less than 15 minutes late, so a cancelled flight counts against it. “(route)” means the best time comes from every carrier on the route rather than this airline alone.
Departure window
The best time of day to leave
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 19 points, against 7 points between the best and worst carrier.
- 5am–8am753 flights94.0%
- 8am–11am630 flights88.4%
- 11am–2pm1,063 flights79.5%
- 2pm–5pm446 flights79.5%
- 5pm–8pm906 flights80.5%
- 8pm–5am300 flights74.8%
Scale runs 65% to 100%.
Book the early departure. Flights leaving between 5am–8am arrive on time 94.0% of the time, against 74.8% for the overnight 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 11am–2pm window is the busiest, with 1,063 flights scheduled in it.
Explore
Filter SEA to SLC 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 SEA to SLC, the best departure window is 5am–8am at 94.0% on time and the worst is 8pm–5am at 74.8%, a wide gap of 19.2 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am94.0%
- 8–11am88.4%
- 11am–2pm79.5%
- 2–5pm79.5%
- 5–8pm80.5%
- 8pm–5am74.8%
best all US flightsScale 60% to 100%.
Across the year
When delays peak on this route
This route's year swings by 17 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 75.3% on time, 17 points below April, 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. July was the busiest month here, with 411 flights.
Across the week, Tuesday is the strongest day at 86.3% on time and Thursday the weakest at 79.1%, a spread of 7 points.
Delay causes
Why this route gets delayed
Carrier accounts for 46% of the 33,000 delay minutes carriers reported here, and the remaining four split what is left.
- 46%Carrier
- 39%Late-arriving aircraft
- 12%National Airspace System
- 2%Extreme weather
39% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. Across 33,000 reported delay minutes here, that single category outweighs weather by 18 to one. The split is drawn from 33,146 reported delay minutes.
The largest share of delay minutes, 46%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 15,000 of the 33,000 delay minutes reported here.
Cancellations are rare at 0.78%, below the national 1.89% and low enough to earn the plus on the grade. Roughly one flight in 100 is called off; the risk here is arriving late, not not arriving.
Connections and stage length
What a delay here actually costs
Badly late arrivals are rare here: only 4.0% 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.
The 689 miles between these two airports put this in the middle of the US network, around two and a half to three hours of block time. That is enough cruise to absorb a ten-minute late pushback and not enough to absorb thirty.
The return leg is a different operation and performs like one: it runs 79.9% on time across 4,098 flights, 4 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 4 points of difference.
The sample behind these figures is 4,098 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 SLC 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. April runs 92.4% on time and August 75.3%, a swing of 17 points. If the dates move at all, move them out of August before you think about anything else. 4,063 completed flights over 12 months sit behind that.
Common questions
SEA to SLC questions
How often is SEA to SLC delayed?
About one flight in six arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 16.6% of the 4,098 flights in this analysis, against 22.7% nationally. Delayed flights are late by about 50 minutes on average.
Which airline is most reliable on SEA to SLC?
Delta Air Lines leads at 86.8% on time across 2,232 flights. Alaska Airlines is at the other end on 79.6%, a gap of 7 points. Sample size matters as much as the percentage: a rate built from a few hundred flights moves around far more than one built from ten thousand.
What time of day has the fewest delays on SEA to SLC?
The 5am–8am departure window is the strongest at 94.0% on time. The 8pm–5am window is the weakest at 74.8%, 19 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 SEA to SLC?
August is the weakest month at 75.3% on time, compared with 92.4% in April. Across the year that is 17 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
- SLC to SEA — the return legseparate record
- Seattle-Tacoma International (SEA) delay statistics
- Salt Lake City International (SLC) delay statistics
- Delta Air Lines on SEA to SLC86.8%
- SkyWest Airlines on SEA to SLC79.7%
- Alaska Airlines on SEA to SLC79.6%
- SEA to LAX, a related route82.0%
- DEN to SLC, a related route78.2%
- SEA to PHX, a related route78.2%
- Delta Air Lines on-time record86.8%
- SkyWest Airlines on-time record79.7%
- Alaska Airlines on-time record79.6%
- 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. SEA to SLC and SLC to SEA 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.