Carrier route record

WNMIA→DEN

Southwest Airlines · Miami to Denver

Flights: 323
Period: July 2025 to June 2026
Share of route: 13%
Carriers: 4

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

Southwest on MIA to DEN draws a D+. Roughly one flight in two arrives at least 15 minutes late, and the typical late arrival is about an hour behind schedule. Build slack into anything you connect to. That rests on 323 flights. The strongest carrier on the route with a full sample, United Airlines, flew 932 at 82.1% on time.

The national on-time rate over the same period is 77.6%, so Southwest on MIA to DEN runs 18 points behind the country as a whole. Across a thousand flights that is about 179 extra late arrivals.

On time

59.7%

Arrivals under 15 minutes late, of 315 completed flights

Avg delay

57 min

Across delayed arrivals only, not all flights

Cancelled

0.00%

National rate is 1.81%

Whole route

77.1%

Every carrier on MIA to DEN, 2,491 flights

These figures cover 323 flights between July 2025 and June 2026. Beyond the headline rate, 14.6% 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

Southwest against every carrier on MIA to DEN

Southwest flew 323 of the 2,491 flights on MIA to DEN, about 13% of it. Its 59.7% on time is 17 points worse than the route as a whole, which runs 77.1%. Ranked by on-time rate it is last of four carriers on the route, where the range runs from Frontier at 82.8% to Southwest at 59.7%. One of those carriers flew fewer than 365 flights here, so treat their positions as rough.

The choice of carrier is not cosmetic here. United Airlines arrives on time 82.1% of the time; American Airlines manages 75.7%. Sample sizes sit next to every figure, because a two-point gap across 885 flights means less than a ten-point one.

On-time performance by carrier on MIA to DEN
Airline	Flights	On time	Avg delay	Cancelled	Grade
Frontier Airlinesthin sample	351	82.8%	112 min	1.42%	B
United Airlines	932	82.1%	68 min	0.11%	B+
American Airlines	885	75.7%	63 min	0.79%	B+
Southwest Airlines (this page)thin sample	323	59.7%	57 min	0.00%	D+

United leads American by 6 points. Real, but small enough that a better departure time on the weaker carrier can outweigh it.

Departure window

When Southwest runs best on this route

Departure time matters more here than the choice of carrier. The gap between the best and worst window is 50 points, against 6 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.

5am–8am33 flights93.9%
8am–11am15 flights—
11am–2pm55 flights58.5%
2pm–5pm184 flights53.9%
5pm–8pm36 flights44.4%
8pm–5am—

Scale runs 35% to 100%. Rows with fewer than 30 flights show a dash.

The 5pm–8pm window is where this operation falls apart: 44.4% on time, against 93.9% 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 2pm–5pm window is the busiest, with 184 flights scheduled in it.

Across the year

Southwest on MIA to DEN through the year

Jul–Sep 202567 flights55.6%
Oct–Dec 202587 flights60.5%
Jan–Mar 202695 flights72.6%
Apr–Jun 202674 flights45.1%

Scale runs 35% to 80%. 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 59.7% on time across 323 flights.

Southwest on MIA to DEN did not run the same all year. Its best quarter was Jan–Mar 2026 at 72.6% on time and its weakest Apr–Jun 2026 at 45.1%, a swing of 27 points on roughly 81 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, Sunday is the strongest day at 61.2% on time and Monday the weakest at 52.0%. 9 points is a smaller lever than departure hour, but it is free.

Delay causes

Why Southwest runs late on this route

Carriers report a reason for every delay minute they cause, in five DOT categories. The split below is by minutes, not by number of flights, so a handful of very long weather delays weighs as much as many short ones. It covers 7,244 reported delay minutes.

Late-arriving aircraft
38%
National Airspace System
32%
Carrier
25%
Extreme weather
5%

38% 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 7,244 reported delay minutes here, that single category outweighs weather by 8 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 7,244 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 93.9% on time here.

Cancellations are rare at 0.00%, below the national 1.81% and low enough to earn the plus on the grade. Almost no flights are called off; the risk here is arriving late, not not arriving.

Connections and stage length

What a delay here costs

For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 14.6% of arrivals land a full hour or more behind schedule, against 8.1% nationally. A 45-minute layover does not survive that, and no amount of walking quickly changes it. Ninety minutes is the honest minimum here, and two hours if the onward flight is on a separate ticket.

At 1,709 miles this is transcontinental flying, and long routes get a quiet structural advantage. Scheduled block time on a flight this length carries more padding in absolute minutes, so a twenty-minute late departure often still becomes an on-time arrival. Read the on-time rate here as slightly flattering next to a short-haul route with the same operational quality.

The return leg is a different operation and performs like one: it runs 63.2% on time across 323 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.

One caution: this is a thin sample. 323 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 Southwest on MIA to DEN

Put together: treat all of this as provisional. 323 flights over twelve months is enough to clear this site's floor and not enough to be confident to better than a couple of points. The 59.7% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 315 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