67% of flights leaving Nantucket (ACK) arrived on time over the past 12 months, 9 points worse than the national average of 76%. About 5 flights leave ACK on a typical day; 6.9% were cancelled. 70% pushed back from the gate on time, so most of the lateness is already there when the flight leaves the gate.
At a glance
- Best hour to fly: noon (69% on time). Worst: 3 p.m. (61%).
- Best month: October (78%). Worst: July (61%).
- Biggest delay cause: late-arriving aircraft (44% of delay minutes).
How late?
The on-time rate treats a flight 20 minutes late the same as one 5 hours late. Here's the split for flights leaving ACK: when a flight was late, it was under 45 minutes late 41% of the time. About 1 in 8 flights landed an hour or more late, and 1 in 34 three hours or more; 6.9% were cancelled outright.
- On time or early67%
- 15–30 min late6.7%
- 30–60 min late6.8%
- 1–2 hours late7.0%
- 2–3 hours late2.6%
- 3+ hours late2.9%
- Diverted0.1%
- Cancelled6.9%
Share of all 2,007 scheduled flights, past 12 months, by arrival time against schedule.
Best time of day to fly out of ACK
ACK is unusually consistent through the day. Flights scheduled to leave at noon arrived on time 69% of the time; at 3 p.m. it was 61%, a 8-point gap. Early planes usually start the day at the airport, so they haven't had a chance to pick up delays elsewhere. By evening a late inbound aircraft, a crew running out of duty hours or an afternoon thunderstorm can push one late flight into the next.
Hour × month
Combine the two and the spread is wider still. The most reliable combination at ACK was a 10 a.m. departure in June (86% on time); the least, 4 p.m. in July (50%). If you can only move one thing, move the hour. Departure hour usually shifts the odds more than the month does.
Each cell: on-time rate for that departure hour in that calendar month, 2023–2026. Find your travel month, then look along the row for the greenest hour.
Best and worst months
July is the hardest month at ACK, with 61% of flights on time across 2023–2026; October is the best at 78%. Summer (June–August) runs 8 points worse than autumn: heavy schedules, peak loads and afternoon thunderstorms. Cancellations peak in July (8.9% of flights).
Airlines at ACK
JetBlue runs 44% of departures from ACK.
| Airline | Departures | On time | Left on time | Cancelled | Typical arrival |
|---|---|---|---|---|---|
| JetBlue | 877 | 63% | 65% | 7.3% | −4 min |
| American Airlines | 527 | 71% | 73% | 5.5% | −10 min |
| Delta Air Lines | 330 | 64% | 71% | 9.4% | −3 min |
| United Airlines | 273 | 74% | 76% | 5.1% | −15 min |
Why flights are late at ACK
Airlines report a cause for every flight that arrives 15 or more minutes late. At ACK, 44% of delay minutes came from late-arriving aircraft: the plane showed up late from its previous flight, so the delay started somewhere else. Next is the air traffic system at 38%. That's why the first flight of the morning is the safest bet: it has no earlier flight to inherit a delay from. Of the 138 cancellations, 28% were blamed on weather, so most were within the airlines’ control or the air traffic system’s.
The average taxi from gate to takeoff is 21 minutes, longer than at most large U.S. airports. Airlines pad schedules for it, but a long queue on a busy afternoon still eats into the buffer.
ACK vs nearby airports
| Airport | Distance | Departures | On time | Cancelled |
|---|---|---|---|---|
| ACK Nantucket Memorial | — | 2,007 | 67% | 6.9% |
| MVY Martha's Vineyard | 30 mi | 1,017 | 66% | 5.7% |
Month by month
Worst cancellation days
The worst single day in the past year was Tuesday, Jul 28, 2026, when 76% of 17 scheduled departures were cancelled. Days like that are usually a major storm, a system outage or a holiday peak hitting bad weather. No average predicts them, so on a stormy forecast, check your airline's travel waivers.
| Date | Departures | Cancelled | On time |
|---|---|---|---|
| Jul 28, 2026 | 17 | 76% | 18% |
| Jul 21, 2026 | 17 | 59% | 6% |
| Jul 18, 2026 | 23 | 57% | 13% |
| Aug 7, 2026 | 19 | 42% | 37% |
| Jul 19, 2026 | 22 | 41% | 36% |
| Jul 7, 2026 | 18 | 39% | 33% |
| Aug 20, 2026 | 19 | 32% | 53% |
| Aug 27, 2026 | 19 | 32% | 47% |
| Aug 3, 2026 | 19 | 26% | 0% |
| Jul 6, 2026 | 19 | 26% | 16% |
Last flights of the day
The last flight of the day is a different bet. Across routes from ACK, each airline's final departure was cancelled 11.2% of the time, against 4.3% for its earlier flights (2.6× as often). Late in the day crews run short on duty hours, aircraft arrive late from elsewhere, and with no later flight to fold passengers into, cancelling is easier for the airline. 3.5% of last flights landed 3+ hours late. The riskiest last flight out was Delta Air Lines to New York (15.4% cancelled).
| Last flight to | Airline | Leaves | Cancelled | 3h+ late | On time |
|---|---|---|---|---|---|
| LGA New York | Delta Air Lines | 4:40 p.m. | 15.4% | 1.8% | 64% |
Each airline's last scheduled departure of the day on a route, on days it flies the route at least twice; past 12 months. Riskiest first.
Tips for flying out of ACK
- Book the earliest departure you can live with. At ACK the noon flights do best.
- Traveling in July? Leave extra slack for anything that can't move: cruises, weddings, the last connection of the day.
- Need to arrive tonight? Don't book the last flight out of ACK; the one before it leaves you a backup.
- Delayed already? Most delays at ACK come from late-arriving aircraft. If your inbound plane is late, your flight will be too, whatever the board says.
Routes from ACK
Least reliable first. Routes with at least 365 flights a year.
| To | Flights | On time | Cancelled | Typical arrival |
|---|---|---|---|---|
| LGA New York | 411 | 67% | 8.5% | −4 min |
Flights into ACK
Arriving rather than leaving? These are the routes into Nantucket Memorial, least reliable first. The weakest is from New York (75% on time).
| From | Flights | On time | Cancelled |
|---|---|---|---|
| LGA New York | 411 | 75% | 4.9% |
Questions about ACK delays
What is the best time to fly out of ACK?
Flights scheduled at noon: over the past year 69% of ACK departures at that hour arrived on time, against 61% at 3 p.m., the worst hour.
What month has the most flight delays at ACK?
July (61% on time). October is the best month (78%).
Why are flights delayed at ACK?
The biggest cause was late-arriving aircraft (44% of delay minutes): the plane showed up late from its previous flight, so the delay started somewhere else. Then the air traffic system (38%).
How often are flights cancelled at ACK?
6.9% of scheduled departures over the past 12 months, peaking in July at 8.9%.
Hours are scheduled local departure times. "On time" means arriving less than 15 minutes late at the destination; cancelled and diverted flights count as not on time. Method.