What Month Has the Most Flight Cancellations?

January. Across the two full years in this data, January flights were cancelled 3.9% of the time on average — more than double the 1.6% national average and the highest of any month. July is the next-worst at 2.7%, and it's the more consistent risk of the two: January's rate swung hard between the two years (3.0% in 2025, 4.7% in 2026), while July stayed in a narrower, dependably bad range both times (2.9% and 2.5%).

• January cancels flights more than any other month, at a 3.9% two-year average — driven by large winter storm systems that can ground entire banks of flights at once.
• July is the most consistently risky month — 2.9% cancelled in 2024 and 2.5% in 2025, a narrower and more dependable range than January's wide 3.0%–4.7% swing.
• September is the most reliable month for completing flights as scheduled, at just 0.6% cancelled — after summer storm season ends and before winter weather begins.
• January's severity varies sharply year to year — 3.0% cancelled in 2025 versus 4.7% in 2026, showing the month's risk depends heavily on how bad that particular winter's storms are.
• A bad cancellation month isn't always a bad delay month — this site tracks the two separately, since cancelled flights are excluded from delay averages. See which month has the worst delays for the delay-specific ranking.

Cancellation rate by month, ranked

Each figure below is a flight-weighted average across the two occurrences of that calendar month in the 24-month data window (June 2024–May 2026), from worst to best:

• January — 3.9% cancelled
• July — 2.7% cancelled
• March — 2.0% cancelled
• February — 1.9% cancelled
• August — 1.6% cancelled
• June — 1.5% cancelled
• November — 1.4% cancelled
• December — 1.1% cancelled
• May — 1.0% cancelled
• October — 0.8% cancelled
• April — 0.9% cancelled
• September — 0.6% cancelled

Why January stands out

Winter storm systems are the most disruptive weather events for US air travel, because a single system can shut down or slow multiple major hub airports on the same day, and the resulting backlog takes days to clear. That makes January cancellations lumpy rather than steady: a mild January can pass with relatively few cancellations, while a January with one or two severe storm systems — like the 4.7% rate seen in 2026 — can pull the whole month's average sharply higher. July's storms, by contrast, tend to be more localized afternoon thunderstorms that cause widespread delays but ground fewer flights outright, which is part of why July shows up as a consistently high-delay month (see below) without cancelling quite as often as a bad January.

Cancellations vs. delays — different seasonal patterns

Cancellations and delays don't always peak in the same months. This site tracks them separately: cancelled and diverted flights are excluded from delay averages entirely (see the methodology), because a cancelled flight has no delay minutes to average in the first place. For the month with the worst delays specifically — as opposed to cancellations — and for the difference between the two concepts generally, see cancelled vs. delayed flight: what's the difference.

Frequently asked questions

What's the least likely month to have your flight cancelled?

September, at a 0.6% average cancellation rate — the lowest of any month in the data, sitting between the end of summer storm season and the start of winter weather.

Is January always the worst month for cancellations?

It was the worst month in one of the two years measured (4.7% in January 2026) and roughly tied with July in the other (3.0% in January 2025 vs. 2.9% in July 2024). July is the more dependable bad month; January is the more volatile one — capable of being merely bad or genuinely severe depending on that winter's storm activity.

Does a cancelled flight count toward a route's average delay?

No. Cancelled and diverted flights are excluded from delay averages on this site and reported as separate rates, matching DOT convention — a flight that never departs doesn't have an arrival delay to measure.

What causes so many cancellations in winter?

Large winter storm systems — snow, ice, and low visibility — can force airports to ground-stop or sharply reduce arrivals and departures for hours at a time. Because major hubs connect to dozens of other airports, a ground stop at one hub can cause airlines to preemptively cancel flights at other airports too, ahead of the storm actually arriving.