Which months have the most flight delays?

In the 12 months from September 2025 to August 2026, flights were most often late in July 2026, when 28.3% arrived 15 or more minutes late, and least often in September 2025 (16.6%). Each bar is one month of the latest year of data, not an average over many years.

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Key facts

Measure: % of flights arriving 15+ minutes late. Written from the data below.

  • Jul 2026 has the highest figure, 28.3%, followed by Aug 2026 (26.9%) and Dec 2025 (26.8%).
  • Sep 2025 has the lowest figure, 16.6%, followed by Feb 2026 (19.8%) and Apr 2026 (20.2%).
  • The highest is 1.7 times the lowest.

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Source and date

Source
U.S. Bureau of Transportation Statistics, Airline On-Time Performance (Reporting Carrier On-Time Performance, 1987–present)
License
Public domain (U.S. government work)
Data as of
Published

Citation

Chartly. “Which months have the most flight delays?” Chart. Data: U.S. Bureau of Transportation Statistics, Airline On-Time Performance (Reporting Carrier On-Time Performance, 1987–present), https://www.transtats.bts.gov/DL_SelectFields.aspx?gnoyr_VQ=FGJ&QO_fu146_anzr=b0-gvzr (data as of August 31, 2026). https://chart.ly/charts/flight-delays-by-month (accessed November 4, 2026).

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The data

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The file has the numbers in this table, with the source, license and date. Please credit the source and Chartly. Developers can also get them as JSON (how).

Month % of flights arriving 15+ minutes late
Sep 2025 16.6
Oct 2025 20.3
Nov 2025 20.6
Dec 2025 26.8
Jan 2026 20.8
Feb 2026 19.8
Mar 2026 24.3
Apr 2026 20.2
May 2026 21.4
Jun 2026 25.7
Jul 2026 28.3
Aug 2026 26.9

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