Best time to fly Nantucket to New York

Every month pooled across the years on record, so "July" means July generally rather than one particular July. Full ACK to JFK record →

Best month

September

84.9% on time · 74 flights

Worst month

June

60.5% on time · 133 flights

Month Flights On time Cancelled When late, by
May 23 60.9% 0% 56 min
June 133 60.5% 6.77% 65 min
July 186 61.6% 7.53% 116 min
August 178 76.5% 6.74% 113 min
September 74 84.9% 1.35% 99 min
October 39 84.6% 0% 74 min

What a seasonal pattern can and cannot tell you

Months differ for reasons that repeat — summer thunderstorms in the American interior, winter fog and de-icing in northern Europe, school holidays filling every seat and leaving no slack in the schedule. Those are real and they come back each year.

What the pattern cannot do is forecast a particular flight. A quiet month has late days and a bad month has punctual ones. Treat this as a way to choose between two dates you are indifferent about, not as a promise.