Route reliability record

SMF→DEN

Sacramento to Denver

Flights: 3,834
Period: July 2025 to June 2026
Distance: 909 mi
Carriers: 3

This route lands a B+, 5 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 55 minutes on average. That is a workable record, not a spotless one. That rests on 3,834 flights, of which United Airlines flew 1,797 at 88.3% on time.

Set against the rest of the country, this route's record is 5 points better than the US average of 77.6%. That gap is worth roughly 49 fewer late arrivals for every thousand flights.

On time

82.5%

Arrivals under 15 minutes late, of 3,801 completed flights

Avg delay

54 min

Across delayed arrivals only, not all flights

Cancelled

0.42%

National rate is 1.81%

Best carrier

United

88.3% on time across 1,797 flights

These figures cover 3,834 flights between July 2025 and June 2026. The median arrival is 5 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 SMF to DEN

The choice of carrier is not cosmetic here. United Airlines arrives on time 88.3% of the time; Southwest Airlines manages 76.8%. Sample sizes sit next to every figure, because a two-point gap across 1,864 flights means less than a ten-point one.

On-time performance by carrier on SMF to DEN
Airline	Flights	On time	Avg delay	Cancelled	Grade
United Airlines	1,797	88.3%	64 min	0.50%	A+
Frontier Airlinesthin sample	173	81.9%	72 min	0.58%	B+
Southwest Airlines	1,864	76.8%	49 min	0.32%	B+

United leads Southwest by 12 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.

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 26 points, against 12 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am735 flights95.1%
8am–11am867 flights91.4%
11am–2pm907 flights80.9%
2pm–5pm772 flights69.4%
5pm–8pm451 flights72.8%
8pm–5am102 flights70.6%

Scale runs 60% to 100%. Rows with fewer than 30 flights show a dash.

Book the early departure. Flights leaving between 5am–8am arrive on time 95.1% of the time, against 69.4% for the afternoon window. That is 26 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 907 flights scheduled in it.

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.

Darker means more delays. Figures are on-time percentages.October best, July worst

July is the worst month at 70.1% on time, 20 points below October, the best at 89.9%. 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 384 flights.

Across the week, Saturday is the strongest day at 86.2% on time and Friday the weakest at 78.8%. 7 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 43% of the 36,000 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
43%
National Airspace System
31%
Carrier
23%
Extreme weather
2%

43% 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 36,000 reported delay minutes here, that single category outweighs weather by 24 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 36,309 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 95.1% on time here.

Cancellations are rare at 0.42%, 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

5.3% 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 are the about 55 minutes kind, which a normal layover absorbs.

The 909 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 73.5% on time across 3,839 flights, 9 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 9 points of difference.

The sample behind these figures is 3,834 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. October runs 89.9% on time and July 70.1%, a swing of 20 points. If the dates move at all, move them out of July before you think about anything else. 3,801 completed flights over 12 months sit behind that.

Common questions

SMF to DEN questions

How often is SMF to DEN 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 17.5% of the 3,834 flights in this analysis, against 22.4% nationally. Delayed flights are late by about 55 minutes on average.

Which airline is most reliable on SMF to DEN?

United Airlines leads at 88.3% on time across 1,797 flights. Southwest Airlines is at the other end on 76.8%, a gap of 12 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 SMF to DEN?

The 5am–8am departure window is the strongest at 95.1% on time. The 2pm–5pm window is the weakest at 69.4%, 26 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 July delays on SMF to DEN?

July is the weakest month at 70.1% on time, compared with 89.9% in October. 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.

Where to go next

Direction matters. SMF to DEN and DEN to SMF 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