Carrier route record

DLSLC→SEA

Delta Air Lines · Salt Lake City to Seattle

Flights: 2,222
Period: July 2025 to June 2026
Share of route: 54%
Carriers: 4

Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Delta Air Lines.

Delta on SLC to SEA lands a B+, 6 points better than the national rate of 77.6%. About one flight in six arrives 15 minutes late or worse, and those flights are late by roughly 55 minutes on average. That is a workable record, not a spotless one. That rests on 2,222 flights. The strongest carrier on the route with a full sample, SkyWest Airlines, flew 419 at 77.3% on time.

Set against the rest of the country, Delta's SLC to SEA record is 6 points better than the US average of 77.6%. That gap is worth roughly 57 fewer late arrivals for every thousand flights.

On time

83.3%

Arrivals under 15 minutes late, of 2,210 completed flights

Avg delay

54 min

Across delayed arrivals only, not all flights

Cancelled

0.54%

National rate is 1.81%

Whole route

80.2%

Every carrier on SLC to SEA, 4,108 flights

These figures cover 2,222 flights between July 2025 and June 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.

Carrier by carrier

Delta against every carrier on SLC to SEA

Delta flew 2,222 of the 4,108 flights on SLC to SEA, most of the route. Its 83.3% on time is 3 points better than the route as a whole, which runs 80.2%. Ranked by on-time rate it is first of four carriers on the route, where the range runs from Delta at 83.3% to Frontier at 69.5%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The two carriers here are closely matched: half a point separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.

On-time performance by carrier on SLC to SEA
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines (this page)	2,222	83.3%	54 min	0.54%	B+
SkyWest Airlines	419	77.3%	73 min	0.00%	B+
Alaska Airlines	1,369	76.7%	46 min	1.83%	B
Frontier Airlinesthin sample	98	69.5%	62 min	3.06%	C−

No carrier stands out. SkyWest tops the table at 77.3%, half a point clear of the bottom, which is inside the range this kind of sample moves year to year.

Flight by flight

Delta flight numbers on SLC to SEA

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 16 points, against half a point between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am134 flights91.7%
8am–11am238 flights92.0%
11am–2pm647 flights87.1%
2pm–5pm404 flights76.4%
5pm–8pm335 flights82.0%
8pm–5am464 flights77.9%

Scale runs 70% to 95%. Rows with fewer than 30 flights show a dash.

Book the morning departure. Flights leaving between 8am–11am arrive on time 92.0% of the time, against 76.4% for the afternoon window. That is 16 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 647 flights scheduled in it.

Across the year

Delta on SLC to SEA through the year

Darker means more delays. Figures are on-time percentages.January best, August worst

August is the worst month at 76.3% on time, 15 points below January, the best at 91.5%. 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. May was the busiest month here, with 207 flights.

Across the week, Saturday is the strongest day at 85.5% on time and Friday the weakest at 80.5%. 5 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Delta runs late on this route

One category carries most of the weight here. Carrier accounts for 50% of the 20,000 delay minutes carriers reported, and the remaining four split what is left. The split is by minutes rather than by flights, so a few very long delays count for as much as many short ones.

Carrier
50%
Late-arriving aircraft
27%
National Airspace System
18%
Extreme weather
5%

The largest share of delay minutes, 50%, falls under carrier control: crew scheduling, maintenance, fuelling, baggage. Unlike weather, that is a management outcome, and it is the category where the gap between two carriers on the same schedule is genuinely earned. It accounts for 9,939 of the 20,000 delay minutes reported here. The split is drawn from 19,834 reported delay minutes.

Cancellations are rare at 0.54%, below the national 1.81% 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 costs

Badly late arrivals are rare here: only 4.4% land an hour or more behind schedule, against 8.1% 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. It is also long enough that the aircraft usually flies three or four legs a day rather than six, which slows how fast delay compounds.

The return leg is a different operation and performs like one: it runs 87.0% on time across 2,219 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 2,222 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 SEA

Put together: the calendar is the biggest lever here, not the carrier or the hour. January runs 91.5% on time and August 76.3%, a swing of 15 points. If the dates move at all, move them out of August before you think about anything else. 2,210 completed flights over 12 months sit behind that.

Where to go next

Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Last updated 15 September 2026; recomputed monthly. How this data is collected.

Key figures