Route reliability record

STL→PHX

St. Louis to Phoenix

Flights: 2,284
Period: July 2025 to June 2026
Distance: 1,262 mi
Carriers: 5

This route sits in the middle of the pack with a B+. Close to three flights in four arrive on time by the DOT's definition, 2 points worse than the national rate of 77.6%. The late ones land a little over an hour behind schedule. That rests on 2,284 flights, of which American Airlines flew 548 at 81.7% on time.

The US average over the same twelve months is 77.6%, so there is little to separate this route from the country as a whole. The variation that matters here is internal: which carrier, and what time of day.

On time

75.3%

Arrivals under 15 minutes late, of 2,270 completed flights

Avg delay

76 min

Across delayed arrivals only, not all flights

Cancelled

0.48%

National rate is 1.81%

Best carrier

American

81.7% on time across 548 flights

These figures cover 2,284 flights between July 2025 and June 2026. Beyond the headline rate, 8.1% of arrivals land a full hour or more behind schedule. That is the number that wrecks a connection, and it is not visible in an on-time percentage alone.

Carrier by carrier

Which airline is most reliable on STL to PHX

The choice of carrier is not cosmetic here. American Airlines arrives on time 81.7% of the time; Southwest Airlines manages 72.2%. Sample sizes sit next to every figure, because a two-point gap across 1,600 flights means less than a ten-point one.

On-time performance by carrier on STL to PHX
Airline	Flights	On time	Avg delay	Cancelled	Grade
Envoy Airthin sample	30	100.0%	—	0.00%	A+
SkyWest Airlinesthin sample	53	83.0%	93 min	0.00%	B+
Frontier Airlinesthin sample	53	82.7%	210 min	1.89%	B
American Airlines	548	81.7%	172 min	0.91%	B+
Southwest Airlines	1,600	72.2%	51 min	0.31%	C+

American leads Southwest by 10 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 34 points, against 10 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am482 flights90.0%
8am–11am451 flights88.4%
11am–2pm183 flights74.6%
2pm–5pm469 flights76.5%
5pm–8pm368 flights55.9%
8pm–5am331 flights56.7%

Scale runs 45% to 95%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 55.9% on time, against 90.0% for the 5am–8am slot. By evening the aircraft flying these rotations have absorbed a full day of small delays and there is no slack left to recover in. The 5am–8am window is the busiest, with 482 flights scheduled in it.

Across the year

When delays peak on this route

This route's year swings by 27 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.January best, June worst

June is the worst month at 57.6% on time, 27 points below January, the best at 84.5%. 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. March was the busiest month here, with 233 flights.

Across the week, Tuesday is the strongest day at 79.4% on time and Sunday the weakest at 69.7%. 10 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 42,000 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
42%
National Airspace System
10%
Extreme weather
4%
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 42,000 reported delay minutes here, that single category outweighs weather by 10 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 42,469 reported delay minutes.

The largest share of delay minutes, 42%, 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 18,000 of the 42,000 delay minutes reported here.

Cancellations are rare at 0.48%, 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

8.1% 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 a little over an hour kind, which a normal layover absorbs.

The 1,262 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 77.8% on time across 2,284 flights, within 3 points 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 2,284 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. January runs 84.5% on time and June 57.6%, a swing of 27 points. If the dates move at all, move them out of June before you think about anything else. 2,270 completed flights over 12 months sit behind that.

Common questions

STL to PHX questions

How often is STL to PHX delayed?

About one flight in four arrive at least 15 minutes late, which is the Department of Transportation's definition of a delayed arrival. That works out to 24.7% of the 2,284 flights in this analysis, against 22.4% nationally. Delayed flights are late by a little over an hour on average.

Which airline is most reliable on STL to PHX?

American Airlines leads at 81.7% on time across 548 flights. Southwest Airlines is at the other end on 72.2%, a gap of 10 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 STL to PHX?

The 5am–8am departure window is the strongest at 90.0% on time. The 5pm–8pm window is the weakest at 55.9%, 34 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 June delays on STL to PHX?

June is the weakest month at 57.6% on time, compared with 84.5% in January. Across the year that is 27 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. STL to PHX and PHX to STL 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