Carrier route record
NKMIA→IAH
Spirit Airlines · Miami to Houston
- Flights
- 440
- Period
- July 2025 to June 2026
- Share of route
- 12%
- Carriers
- 6
Historical statistics for July 2025 to June 2026, not live status. For today’s flights, check with Spirit Airlines.
Spirit on MIA to IAH sits in the middle of the pack with a C. About seven flights in ten arrive on time by the DOT's definition, 8 points worse than the national rate of 77.6%. The late ones land an hour and a half behind schedule. That rests on 440 flights. The strongest carrier on the route with a full sample, United Airlines, flew 1,479 at 85.9% on time.
The national on-time rate over the same period is 77.6%, so Spirit on MIA to IAH runs 8 points behind the country as a whole. Across a thousand flights that is about 79 extra late arrivals.
Key figures
On time
69.7%
Arrivals under 15 minutes late, of 426 completed flights
Avg delay
87 min
Across delayed arrivals only, not all flights
Cancelled
2.73%
National rate is 1.81%
Whole route
77.2%
Every carrier on MIA to IAH, 3,737 flights
These figures cover 440 flights between July 2025 and June 2026. Beyond the headline rate, 15.0% 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
Spirit against every carrier on MIA to IAH
Spirit flew 440 of the 3,737 flights on MIA to IAH, about 12% of it. Its 69.7% on time is 8 points worse than the route as a whole, which runs 77.2%. Ranked by on-time rate it is number five of six carriers on the route, where the range runs from Envoy at 86.9% to Republic at 64.3%. Three 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 85.9% of the time; American Airlines manages 70.1%. Sample sizes sit next to every figure, because a two-point gap across 1,527 flights means less than a ten-point one.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| Envoy Airthin sample | 122 | 86.9% | 39 min | 0.00% | A+ |
| United Airlines | 1,479 | 85.9% | 91 min | 0.61% | A+ |
| Frontier Airlinesthin sample | 155 | 78.4% | 97 min | 1.29% | B |
| American Airlines | 1,527 | 70.1% | 72 min | 1.24% | C |
| Spirit Airlines (this page) | 440 | 69.7% | 87 min | 2.73% | C |
| Republic Airwaysthin sample | 14 | 64.3% | 133 min | 0.00% | D+ |
The spread between United and American is 16 points, wide enough that it should decide the booking. On a hundred trips that is 16 more arrivals inside the on-time window.
Departure window
When Spirit runs best on this route
Departure time matters more here than the choice of carrier. The gap between the best and worst window is 20 points, against 16 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am48 flights72.3%
- 8am–11am8 flights—
- 11am–2pm74 flights80.8%
- 2pm–5pm72 flights60.6%
- 5pm–8pm107 flights68.9%
- 8pm–5am131 flights68.6%
Scale runs 50% to 85%. Rows with fewer than 30 flights show a dash.
The best window here is not the first bank but the 11am–2pm slot at 80.8% on time, ahead of 2pm–5pm at 60.6%. Where the curve peaks mid-day rather than at dawn, the constraint is usually congestion at one end rather than the aircraft's own rotation. The 8pm–5am window is the busiest, with 131 flights scheduled in it.
Across the year
Spirit on MIA to IAH through the year
December is the weak month at 66.0% on time, against 77.6% in July. 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 60 flights.
Across the week, Tuesday is the strongest day at 77.2% on time and Sunday the weakest at 59.4%. 18 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Spirit runs late on this route
One category carries most of the weight here. National Airspace System accounts for 47% of the 11,000 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.
- 47%National Airspace System
- 34%Late-arriving aircraft
- 16%Carrier
- 4%Extreme weather
- 0%Security
47% of delay minutes are charged to the National Airspace System: air traffic volume, runway configuration, ground stops. No carrier can price its way out of that, which is why airport choice moves the number here more than carrier choice does. That is 5,220 minutes out of 11,000, against a national NAS share of 21%. The split is drawn from 11,168 reported delay minutes.
Cancellations run at 2.73%, against 1.81% nationally. That is roughly one flight in 40 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
For anyone connecting, the number to weigh is not the on-time rate but the tail behind it. 15.0% 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.
The 964 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 70.7% on time across 441 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. 440 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 Spirit on MIA to IAH
Put together: treat all of this as provisional. 440 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 69.7% headline is the most reliable number on the page; the hour and month splits below it are built on a few dozen flights each. 426 completed flights over 12 months sit behind that.
Related
Where to go next
- MIA to IAH, every carrier
- Spirit on IAH to MIA, the return leg
- Envoy Air on MIA to IAH86.9%
- United Airlines on MIA to IAH85.9%
- Frontier Airlines on MIA to IAH78.4%
- American Airlines on MIA to IAH70.1%
- Spirit Airlines network-wide record
- Miami International (MIA) delay statistics
- George Bush Intercontinental (IAH) delay statistics
- The US routes with the most cancellations
- Why the first flight of the morning is statistically safest
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.