Route reliability record

SEA→SMF

Seattle to Sacramento

Flights: 4,407
Period: July 2025 to June 2026
Distance: 605 mi
Carriers: 3

This route lands a B+, 4 points better than the national rate of 77.6%. About one flight in six arrive 15 minutes late or worse, and those flights are late by about 50 minutes on average. That is a workable record, not a spotless one. That rests on 4,407 flights, of which SkyWest Airlines flew 1,941 at 89.3% on time.

SkyWest Airlines is the most reliable of the three carriers covered here at 89.3% on time across 1,941 flights.

On time

81.9%

Arrivals under 15 minutes late, of 4,379 completed flights

Avg delay

50 min

Across delayed arrivals only, not all flights

Cancelled

0.41%

National rate is 1.81%

Best carrier

SkyWest

89.3% on time across 1,941 flights

These figures cover 4,407 flights between July 2025 and June 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.

Carrier by carrier

Which airline is most reliable on SEA to SMF

The choice of carrier is not cosmetic here. SkyWest Airlines arrives on time 89.3% of the time; Southwest Airlines manages 71.9%. Sample sizes sit next to every figure, because a two-point gap across 1,156 flights means less than a ten-point one.

On-time performance by carrier on SEA to SMF
Airline	Flights	On time	Avg delay	Cancelled	Grade
SkyWest Airlines	1,941	89.3%	62 min	0.26%	A+
Alaska Airlines	1,310	79.8%	44 min	0.61%	B+
Southwest Airlines	1,156	71.9%	48 min	0.43%	C+

The spread between SkyWest and Southwest is 17 points, wide enough that it should decide the booking. On a hundred trips that is 17 more arrivals inside the on-time window.

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 21 points, against 17 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am467 flights93.5%
8am–11am1,078 flights90.0%
11am–2pm613 flights75.9%
2pm–5pm815 flights80.9%
5pm–8pm525 flights72.2%
8pm–5am909 flights77.0%

Scale runs 65% to 100%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 93.5% of the time, against 72.2% for the evening window. That is 21 points of difference for no extra money, and it comes from the same aircraft having had no earlier flight to fall behind on. The 8am–11am window is the busiest, with 1,078 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 14 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.

Darker means more delays. Figures are on-time percentages.April best, December worst

December is the weak month at 73.4% on time, against 87.5% in April. 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. July was the busiest month here, with 455 flights.

Across the week, Tuesday is the strongest day at 85.1% on time and Friday the weakest at 78.7%. 6 points is a smaller lever than departure hour, but it is free.

Delay causes

Why this route gets delayed

One category carries most of the weight here. Late-arriving aircraft accounts for 44% of the 40,000 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.

Late-arriving aircraft
44%
Carrier
41%
National Airspace System
8%
Extreme weather
7%
Security
0%

44% 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 40,000 reported delay minutes here, that single category outweighs weather by 6 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 39,661 reported delay minutes.

The largest share of delay minutes, 41%, 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 16,000 of the 40,000 delay minutes reported here.

Cancellations are rare at 0.41%, 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 actually costs

Badly late arrivals are rare here: only 4.3% 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 605 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 82.7% on time across 4,416 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.

The sample behind these figures is 4,407 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 this route

Put together: the calendar is the biggest lever here, not the carrier or the hour. April runs 87.5% on time and December 73.4%, a swing of 14 points. If the dates move at all, move them out of December before you think about anything else. 4,379 completed flights over 12 months sit behind that.

Common questions

SEA to SMF questions

How often is SEA to SMF delayed?

About one flight in six arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 18.1% of the 4,407 flights in this analysis, against 22.4% nationally. Delayed flights are late by about 50 minutes on average.

Which airline is most reliable on SEA to SMF?

SkyWest Airlines leads at 89.3% on time across 1,941 flights. Southwest Airlines is at the other end on 71.9%, a gap of 17 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 SMF?

The 5am–8am departure window is the strongest at 93.5% on time. The 5pm–8pm window is the weakest at 72.2%, 21 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 December delays on SEA to SMF?

December is the weakest month at 73.4% on time, compared with 87.5% in April. Across the year that is 14 points between the best and worst months. Moving flexible dates out of that month is one of the few things that reliably helps.

Where to go next

Direction matters. SEA to SMF and SMF to SEA are scored separately because they are separate operations, with different departure banks and different aircraft. Compare the return leg.

Source: US DOT Bureau of Transportation Statistics, on-time performance data, July 2025 to June 2026. Updated monthly. How this data is collected.

Key figures