Carrier route record

F9LAX→SEA

Frontier Airlines · Los Angeles to Seattle

Flights: 276
Period: July 2025 to June 2026
Share of route: 4%
Carriers: 6

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

Frontier on LAX to SEA lands a B−, 2 points better than the national rate of 77.6%. About one flight in five arrives 15 minutes late or worse, and those flights are late by a little over an hour on average. That is a workable record, not a spotless one. That rests on 276 flights. The strongest carrier on the route with a full sample, Delta Air Lines, flew 2,224 at 86.8% on time.

Delta Air Lines is the most reliable of the four carriers covered here at 86.8% on time across 2,224 flights.

On time

79.7%

Arrivals under 15 minutes late, of 266 completed flights

Avg delay

76 min

Across delayed arrivals only, not all flights

Cancelled

3.62%

National rate is 1.81%

Whole route

85.4%

Every carrier on LAX to SEA, 7,424 flights

These figures cover 276 flights between July 2025 and June 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.

Carrier by carrier

Frontier against every carrier on LAX to SEA

Frontier flew 276 of the 7,424 flights on LAX to SEA, about 4% of it. Its 79.7% on time is 6 points worse than the route as a whole, which runs 85.4%. Ranked by on-time rate it is last of six carriers on the route, where the range runs from Delta at 86.8% to Frontier at 79.7%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The four carriers here are closely matched: 2 points 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 LAX to SEA
Airline	Flights	On time	Avg delay	Cancelled	Grade
Delta Air Lines	2,224	86.8%	76 min	0.76%	A+
Alaska Airlines	3,279	85.2%	49 min	1.10%	A
United Airlines	395	85.0%	47 min	0.51%	A+
SkyWest Airlines	1,239	84.6%	82 min	0.65%	B+
American Airlinesthin sample	11	81.8%	159 min	0.00%	B+
Frontier Airlines (this page)thin sample	276	79.7%	76 min	3.62%	B−

No carrier stands out. Delta tops the table at 86.8%, 2 points clear of the bottom, which is inside the range this kind of sample moves year to year.

Flight by flight

Frontier flight numbers on LAX to SEA

F9 117715:1579.5% · 269 flights

Departure window

When Frontier 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 276 flights.

5am–8am—
8am–11am53 flights84.3%
11am–2pm27 flights—
2pm–5pm149 flights80.4%
5pm–8pm21 flights—
8pm–5am26 flights—

Scale runs 70% to 90%. Rows with fewer than 30 flights show a dash.

The 8am–11am window is the strongest at 84.3% on time. The full set of windows spans 4 points.

Across the year

Frontier on LAX to SEA through the year

Jul–Sep 202551 flights76.0%
Oct–Dec 202568 flights68.3%
Jan–Mar 202666 flights88.9%
Apr–Jun 202691 flights83.3%

Scale runs 60% to 95%. Rows with fewer than 30 flights show a dash.

Monthly volumes are too low here to break the year into twelve reliable readings. What the twelve-month total says is 79.7% on time across 276 flights.

Frontier on LAX to SEA did not run the same all year. Its best quarter was Jan–Mar 2026 at 88.9% on time and its weakest Oct–Dec 2025 at 68.3%, a swing of 21 points on roughly 69 flights a quarter. The twelve-month rate averages over that, so if you are flying in a weak quarter the quarter's own figure is the better guide.

Across the week, Saturday is the strongest day at 89.6% on time and Sunday the weakest at 71.8%. 18 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Frontier runs late on this route

One category carries most of the weight here. Late-arriving aircraft accounts for 67% of the 4,120 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.

Late-arriving aircraft
67%
Carrier
19%
National Airspace System
13%
Extreme weather
1%

67% of delay minutes trace back to a late-arriving aircraft, meaning the plane was already behind before it got here. That is a cascade, and cascades start small and grow through the day. Across 4,120 reported delay minutes here, that single category outweighs weather by 66 to one. It is the strongest argument for booking the first departure of the morning, when the aircraft has been sitting at the gate overnight with nothing to inherit. The split is drawn from 4,120 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 84.3% on time here.

Cancellations run at 3.62%, against 1.81% nationally. That is about one flight in 30 cancelled outright. A cancelled flight is invisible in every on-time figure on this page, so the punctuality numbers above describe only the flights that actually operated.

Connections and stage length

What a delay here costs

6.8% of arrivals land an hour or more late, close to the national 8.1%. That is the figure that decides a connection, and it says a 60 to 75 minute layover is reasonable here while anything under 45 minutes is a bet. Most delays on this route last a little over an hour, which a normal layover absorbs.

The 954 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 runs 78.9% on time across 276 flights, within about a point of this direction. The two legs are scored separately because they usually differ; on this city pair they happen not to.

One caution: this is a thin sample. 276 flights over twelve months is enough to clear this site's floor but not enough to pin the rate down tightly, and a single bad week moves it by more than a point. Treat the grade as a rough reading.

What to do with this

Booking Frontier on LAX to SEA

Put together: the delay figures matter less here than the 3.62% cancellation rate. A late arrival costs you a little over an hour; a cancelled flight costs you the day. Book the 8am–11am departure so there is still a schedule behind you if it goes wrong, and treat a same-day connection as optimistic. 266 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