Carrier route record
NKMIA→BOS
Spirit Airlines · Miami to Boston
- Flights
- 186
- Period
- July 2025 to June 2026
- Share of route
- 5%
- 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 BOS earns an F−, which is as low as this site's scale goes for a reason. Only 54.3% of flights arrive inside the 15-minute window, 23 points worse than the national rate of 77.6%. Late arrivals average a little over an hour. Treat any tight connection here as a coin flip. That rests on 186 flights. The strongest carrier on the route with a full sample, American Airlines, flew 2,230 at 70.7% on time.
The national on-time rate over the same period is 77.6%, so Spirit on MIA to BOS runs 23 points behind the country as a whole. Across a thousand flights that is about 233 extra late arrivals.
Key figures
On time
54.3%
Arrivals under 15 minutes late, of 173 completed flights
Avg delay
70 min
Across delayed arrivals only, not all flights
Cancelled
6.45%
National rate is 1.81%
Whole route
69.7%
Every carrier on MIA to BOS, 3,415 flights
These figures cover 186 flights between July 2025 and June 2026. Beyond the headline rate, 27.2% 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 BOS
Spirit flew 186 of the 3,415 flights on MIA to BOS, about 5% of it. Its 54.3% on time is 15 points worse than the route as a whole, which runs 69.7%. Ranked by on-time rate it is last of six carriers on the route, where the range runs from Envoy at 100.0% to Spirit at 54.3%. Three of those carriers flew fewer than 365 flights here, so treat their positions as rough.
The two carriers here are closely matched: half a point 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 |
|---|---|---|---|---|---|
| Envoy Airthin sample | 1 | 100.0% | — | 0.00% | A+ |
| Republic Airwaysthin sample | 21 | 81.0% | 96 min | 0.00% | B+ |
| American Airlines | 2,230 | 70.7% | 71 min | 1.75% | C |
| Delta Air Lines | 888 | 70.0% | 78 min | 2.93% | C |
| JetBlue Airwaysthin sample | 89 | 66.7% | 68 min | 5.62% | C− |
| Spirit Airlines (this page)thin sample | 186 | 54.3% | 70 min | 6.45% | F− |
No carrier stands out. American tops the table at 70.7%, half a point 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 is the single lever a traveller controls, and it moves the odds more than most people expect. Each bar below is the on-time rate for flights scheduled to leave inside that window, across 186 flights.
- 5am–8am1 flights—
- 8am–11am61 flights62.5%
- 11am–2pm80 flights59.2%
- 2pm–5pm16 flights—
- 5pm–8pm—
- 8pm–5am28 flights—
Scale runs 50% to 70%. Rows with fewer than 30 flights show a dash.
The 8am–11am window is the strongest at 62.5% on time. The full set of windows spans 3 points.
Across the year
Spirit on MIA to BOS through the year
- Jul–Sep 202523 flights—
- Oct–Dec 202510 flights—
- Jan–Mar 2026112 flights54.5%
- Apr–Jun 202641 flights50.0%
Scale runs 40% to 60%. 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 54.3% on time across 186 flights.
Split by quarter, Spirit on MIA to BOS logged 23 flights in Jul–Sep 2025, 10 flights in Oct–Dec 2025, 112 flights in Jan–Mar 2026 and 41 flights in Apr–Jun 2026. Fewer than three of those quarters carried the 30 completed flights this site needs before printing a rate, so the 54.3% annual figure is the one to use.
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 5,553 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
- 37%Late-arriving aircraft
- 15%Carrier
- 1%Extreme weather
37% 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 5,553 reported delay minutes here, that single category outweighs weather by 37 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 5,553 reported delay minutes.
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 2,591 minutes out of 5,553, against a national NAS share of 21%.
Cancellations run at 6.45%, against 1.81% nationally. That is about one flight in fifteen 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. 27.2% 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 1,258 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 54.0% on time across 187 flights, within half 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. 186 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 BOS
Put together: the delay figures matter less here than the 6.45% cancellation rate. A late arrival costs you a little over an hour; a cancelled flight costs you the day. Book the 8am–11am departure so there is still a schedule behind you if it goes wrong, and treat a same-day connection as optimistic. 173 completed flights over 12 months sit behind that.
Related
Where to go next
- MIA to BOS, every carrier
- Spirit on BOS to MIA, the return leg
- American Airlines on MIA to BOS70.7%
- Delta Air Lines on MIA to BOS70.0%
- Spirit Airlines network-wide record
- Miami International (MIA) delay statistics
- Boston Logan International (BOS) 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.