Carrier route record
NKIAH→MIA
Spirit Airlines · Houston to Miami
- Flights
- 441
- 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 IAH to MIA sits in the middle of the pack with a C−. About seven flights in ten arrive on time by the DOT's definition, 7 points worse than the national rate of 77.6%. The late ones land a little over an hour behind schedule. That rests on 441 flights. The strongest carrier on the route with a full sample, United Airlines, flew 1,479 at 80.3% on time.
The national on-time rate over the same period is 77.6%, so Spirit on IAH to MIA runs 7 points behind the country as a whole. Across a thousand flights that is about 69 extra late arrivals.
Key figures
On time
70.7%
Arrivals under 15 minutes late, of 427 completed flights
Avg delay
79 min
Across delayed arrivals only, not all flights
Cancelled
3.17%
National rate is 1.81%
Whole route
77.8%
Every carrier on IAH to MIA, 3,736 flights
These figures cover 441 flights between July 2025 and June 2026. Beyond the headline rate, 14.5% 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 IAH to MIA
Spirit flew 441 of the 3,736 flights on IAH to MIA, about 12% of it. Its 70.7% on time is 7 points worse than the route as a whole, which runs 77.8%. Ranked by on-time rate it is number four of six carriers on the route, where the range runs from United at 80.3% to Republic at 64.3%. Three of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The two carriers here are closely matched: 2 points separate the best from the worst. At that spread, schedule and price are better tie-breakers than reliability. Sample sizes are shown so you can see which rows are worth weighing.
| Airline | Flights | On time | Avg delay | Cancelled | Grade |
|---|---|---|---|---|---|
| United Airlines | 1,479 | 80.3% | 61 min | 0.41% | B+ |
| Envoy Airthin sample | 122 | 78.5% | 52 min | 0.00% | B+ |
| American Airlines | 1,526 | 78.3% | 111 min | 1.31% | B |
| Spirit Airlines (this page) | 441 | 70.7% | 79 min | 3.17% | C− |
| Frontier Airlinesthin sample | 154 | 68.9% | 142 min | 1.95% | C |
| Republic Airwaysthin sample | 14 | 64.3% | 173 min | 0.00% | D+ |
No carrier stands out. United tops the table at 80.3%, 2 points clear of the bottom, which is inside the range this kind of sample moves year to year.
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 28 points, against 2 points between the best and worst carrier. Each bar is the on-time rate for flights scheduled inside that window.
- 5am–8am79 flights85.7%
- 8am–11am38 flights84.2%
- 11am–2pm10 flights—
- 2pm–5pm153 flights69.8%
- 5pm–8pm123 flights57.3%
- 8pm–5am38 flights66.7%
Scale runs 50% to 90%. Rows with fewer than 30 flights show a dash.
The 5pm–8pm window is where this operation falls apart: 57.3% on time, against 85.7% 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 153 flights scheduled in it.
Across the year
Spirit on IAH to MIA through the year
January is the weak month at 58.1% on time, against 78.3% in December. 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 61 flights.
Across the week, Wednesday is the strongest day at 80.8% on time and Friday the weakest at 60.3%. 21 points is a smaller lever than departure hour, but it is free.
Delay causes
Why Spirit 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 9,920 reported delay minutes.
- 39%National Airspace System
- 32%Carrier
- 27%Late-arriving aircraft
- 3%Extreme weather
- 0%Security
39% 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 3,820 minutes out of 9,920, against a national NAS share of 21%. The split is drawn from 9,920 reported delay minutes.
Cancellations run at 3.17%, against 1.81% nationally. That is about one flight in 30 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. 14.5% 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 69.7% on time across 440 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. 441 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 IAH to MIA
Put together: the delay figures matter less here than the 3.17% cancellation rate. A late arrival costs you a little over an hour; a cancelled flight costs you the day. Book the 5am–8am departure so there is still a schedule behind you if it goes wrong, and treat a same-day connection as optimistic. 427 completed flights over 12 months sit behind that.
Related
Where to go next
- IAH to MIA, every carrier
- Spirit on MIA to IAH, the return leg
- United Airlines on IAH to MIA80.3%
- Envoy Air on IAH to MIA78.5%
- American Airlines on IAH to MIA78.3%
- Frontier Airlines on IAH to MIA68.9%
- Spirit Airlines network-wide record
- George Bush Intercontinental (IAH) delay statistics
- Miami International (MIA) delay statistics
- The US routes with the most cancellations
- The best time of day to fly, according to 7.04 million flight records
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.