Route reliability record
SLC→SEA
Salt Lake City to Seattle
- Flights
- 4,098
- Period
- September 2025 to August 2026
- Distance
- 689 mi
- Carriers
- 4
This route lands a B+, 3 points better than the national rate of 77.3%. About one flight in five arrives 15 minutes late or worse, and those flights are late by about an hour on average. That rests on 4,098 SLC to SEA flights, of which Delta Air Lines flew 2,234 at 82.7% on time.
Best time to fly SLC to SEA: a 5am–8am departure, ideally on a Tuesday. Flights in that window arrived on time 91.5% of the time and Tuesday flights 84.3%, against 79.9% for the route overall.
Delta Air Lines is the most reliable of the three carriers covered here at 82.7% on time across 2,234 flights.
Key figures
On time
79.9%
Arrivals under 15 minutes late, of 4,061 completed flights
Avg delay
55 min
Across delayed arrivals only, not all flights
Cancelled
0.81%
National rate is 1.89%
Best carrier
Delta
82.7% on time across 2,234 flights
These figures cover 4,098 flights between September 2025 and August 2026. The median arrival is 6 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 SLC to SEA
The choice of carrier is not cosmetic here. Delta Air Lines arrives on time 82.7% of the time; SkyWest Airlines manages 75.7%. Sample sizes sit next to every figure, because a two-point gap across 366 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Delta Air Lines | 2,234 | 82.7% | 53 min | 0.49% | B+ |
| Alaska Airlines | 1,421 | 77.3% | 48 min | 1.41% | B |
| SkyWest Airlines | 366 | 75.7% | 89 min | 0.00% | B+ |
| Frontier Airlinesthin sample | 77 | 65.3% | 64 min | 2.60% | C |
Delta leads SkyWest by 7 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.
Flight by flight
Flights on SLC to SEA
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 Salt Lake City to Seattle
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. SLC → SEASalt Lake City to Seattle | Delta Air Lines | 82.3% | 82.7% | 0.49% | 8am–11am, Tue | DL 2874 07:45 |
| 2. SLC → SEASalt Lake City to Seattle | Alaska Airlines | 76.2% | 77.3% | 1.41% | 5am–8am, Tue | AS 796 11:17 |
| 3. SLC → SEASalt Lake City to Seattle | SkyWest Airlines | 75.7% | 75.7% | 0.00% | 5am–8am, Wed | — |
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–8am522 flights91.5%
- 8am–11am461 flights75.3%
- 11am–2pm1,110 flights84.3%
- 2pm–5pm820 flights76.5%
- 5pm–8pm525 flights77.2%
- 8pm–5am660 flights73.0%
Scale runs 65% to 95%.
Book the early departure. Flights leaving between 5am–8am arrive on time 91.5% of the time, against 73.0% 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 1,110 flights scheduled in it.
Explore
Filter SLC to SEA 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 SLC to SEA, the best departure window is 5am–8am at 91.5% on time and the worst is 8pm–5am at 73.0%, a wide gap of 18.5 points. All US flights leaving 5am–8am ran 89.3%.
- 5–8am91.5%
- 8–11am75.3%
- 11am–2pm84.3%
- 2–5pm76.5%
- 5–8pm77.2%
- 8pm–5am73.0%
best all US flightsScale 60% to 95%.
Across the year
When delays peak on this route
This route's year swings by 20 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 69.0% on time, 20 points below April, the best at 89.2%. 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 84.3% on time and Monday the weakest at 76.7%, a spread of 8 points.
Delay causes
Why this route gets delayed
Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 45,000 reported delay minutes.
- 41%Carrier
- 31%Late-arriving aircraft
- 22%National Airspace System
- 6%Extreme weather
- 0%Security
The largest share of delay minutes, 41%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. It accounts for 19,000 of the 45,000 delay minutes reported here. The split is drawn from 44,870 reported delay minutes.
The practical consequence: the 5am–8am departure is the one that starts clean. Its aircraft has no earlier leg to be late from, which is exactly why that window shows 91.5% on time here.
Cancellations are rare at 0.81%, 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 4.9% 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 83.4% on time across 4,098 flights, 4 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 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 SEA 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 89.2% on time and August 69.0%, a swing of 20 points. If the dates move at all, move them out of August before you think about anything else. 4,061 completed flights over 12 months sit behind that.
Common questions
SLC to SEA questions
How often is SLC to SEA delayed?
About one flight in five arrives at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 20.1% of the 4,098 flights in this analysis, against 22.7% nationally. Delayed flights are late by about an hour on average.
Which airline is most reliable on SLC to SEA?
Delta Air Lines leads at 82.7% on time across 2,234 flights. SkyWest Airlines is at the other end on 75.7%, 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 SLC to SEA?
The 5am–8am departure window is the strongest at 91.5% on time. The 8pm–5am window is the weakest at 73.0%, 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 SLC to SEA?
August is the weakest month at 69.0% on time, compared with 89.2% in April. Across the year that is 20 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
- SEA to SLC — the return legseparate record
- Salt Lake City International (SLC) delay statistics
- Seattle-Tacoma International (SEA) delay statistics
- Delta Air Lines on SLC to SEA82.7%
- Alaska Airlines on SLC to SEA77.3%
- SkyWest Airlines on SLC to SEA75.7%
- SLC to DEN, a related route79.0%
- LAX to SEA, a related route85.0%
- SLC to PHX, a related route83.5%
- Delta Air Lines on-time record82.7%
- Alaska Airlines on-time record77.3%
- SkyWest Airlines on-time record75.7%
- 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
Direction matters. SLC to SEA and SEA to SLC 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.