Busy Months Aren't Always Late Months: Volume vs. On-Time Rate by Month
July and October carry nearly the same arrivals, yet July runs 12.4 points later. Volume set against on-time rate for each calendar month, DOT record.
July carried the most arrivals per year of any calendar month in the U.S. DOT on-time record, and it ran the latest: 71.4 percent of arrivals on time across June 2023 through July 2026. October carried almost the same load — about 1.30 million arrivals per year against July's 1.31 million — and ran 83.8 percent on time. Volume differs by about 1.2 percent between those two months. The on-time rate differs by 12.4 points.
That gap is the reason "fly when it's quiet" is a weaker rule than it sounds. This guide sets each calendar month's traffic beside its on-time rate, using the record behind the Best Month to Fly tool.
The data behind the comparison
Every figure below comes from the U.S. DOT / Bureau of Transportation Statistics Marketing Carrier On-Time Performance filing (TranStats table 236), pooled across all reporting carriers and airports. The record OnTimeIndex serves runs 38 months, June 2023 through July 2026. "On time" is the federal rule, used unchanged: a flight that arrives less than 15 minutes after its published arrival time (14 CFR § 234.2). Fourteen minutes late is on time; fifteen is not.
One detail changes how volume must be read. Because the record starts in June and ends in July, June and July each appear four times (2023, 2024, 2025, 2026) and every other month appears three times. The raw arrival counts for June and July are therefore larger simply because they cover an extra year. The table divides each month's pooled arrivals by the number of years it covers, so the months can be compared.
| Calendar month | Arrival on-time rate | Arrivals filed, pooled | Years pooled | Arrivals per year |
|---|---|---|---|---|
| January | 78.8% | 3,420,542 | 3 | about 1.14 million |
| February | 81.3% | 3,305,226 | 3 | about 1.10 million |
| March | 78.6% | 3,861,864 | 3 | about 1.29 million |
| April | 80.5% | 3,810,050 | 3 | about 1.27 million |
| May | 76.4% | 3,929,504 | 3 | about 1.31 million |
| June | 73.7% | 5,114,350 | 4 | about 1.28 million |
| July | 71.4% | 5,250,046 | 4 | about 1.31 million |
| August | 77.7% | 3,862,090 | 3 | about 1.29 million |
| September | 83.3% | 3,659,906 | 3 | about 1.22 million |
| October | 83.8% | 3,890,326 | 3 | about 1.30 million |
| November | 83.8% | 3,643,790 | 3 | about 1.21 million |
| December | 78.7% | 3,721,968 | 3 | about 1.24 million |
Source: BTS Marketing Carrier On-Time Performance, June 2023 – July 2026, all reporting airports combined. "Arrivals per year" is the pooled count divided by years pooled, a simple average that ignores growth from one year to the next.
Worked example: July against October
July averages about 1,312,500 arrivals per year in this record. October averages about 1,296,800. July is 1.2 percent busier.
The on-time rates are 71.4 percent and 83.8 percent. Put another way, across the record about 28.6 of every 100 July arrivals did not arrive on time, against about 16.2 of every 100 in October.
If traffic volume were the main thing separating the two months, a 1.2 percent difference in load could not produce a 12.4-point difference in the rate. Something else about the two months is doing most of the work.
A second pair: May against October
May averages about 1,309,800 arrivals per year, October about 1,296,800 — again within about 1 percent. May's on-time rate is 76.4 percent and October's is 83.8 percent, a 7.4-point gap between two months of near-identical volume.
The quiet months are not the best months
The lightest months in the record are February (about 1.10 million arrivals per year) and January (about 1.14 million). February ran 81.3 percent on time and January 78.8 percent. Both are below September (83.3 percent), October (83.8 percent) and November (83.8 percent), each of which carries more traffic than January or February.
So the lightest months are not the punctual ones. Among the three highest-rated months, September and November rank ninth and tenth of twelve on arrivals per year, while October ranks third. A rule that ranks months by how full the system is would get several of these wrong.
What this comparison does not show
- It does not say what causes the gap. This file carries no monthly split of delay causes, so this guide makes no claim about why July or May run later than October. The federal filing does report five cause categories — carrier, weather, National Air System, security and late-arriving aircraft — and the guide on what the DOT delay causes mean explains each one.
- A monthly total is not the load at your airport or your hour. A month's system-wide arrivals can be evenly spread or bunched into a few hours at a few airports. This comparison cannot tell those apart.
- It is arrivals, all airports together. The Best Month to Fly tool reports departures for one airport at a time, and airport curves can differ a lot from the national one.
- It leaves out cancellations and diversions. Read those next to any on-time rate, as covered in the guide on cancellation rate versus on-time rate.
- It is history, not a forecast. These are base rates from June 2023 through July 2026. They say nothing about a specific date or flight.
How to use this before you book
Treat "which month is busiest" and "which month runs late" as two separate questions. The Best Month to Fly tool answers the second one directly: enter a U.S. airport and it shows the on-time departure rate for each calendar month, pooled across the years the site serves, with a year-by-year table so one unusually bad season is visible instead of averaged away. For the seasonal pattern on a specific route, see seasonal route reliability.
Frequently asked questions
Is the busiest month of the year the least punctual?
In this record, yes for July, but the link is loose. July has the highest average arrivals per year (about 1.31 million) and the lowest arrival on-time rate (71.4 percent) across June 2023 through July 2026. May carries almost the same volume (about 1.31 million) at 76.4 percent, so volume alone does not set the rate.
Why does the record show June and July with so many more arrivals?
Because the record covers June 2023 through July 2026, June and July each appear in four years while every other month appears in three. Divided by years pooled, their volumes fall in line with the other busy months.
Which months had the highest on-time arrival rate?
October and November, each at 83.8 percent, across June 2023 through July 2026. September followed at 83.3 percent.
Does a lighter month mean fewer late flights?
Not in this record. February had the fewest arrivals per year (about 1.10 million) and ran 81.3 percent on time, below the 83.8 percent of October, which carried about 1.30 million arrivals per year.
Last reviewed: September 2026. Analysis by Eric, OnTimeIndex founder.
Sources
Informational only — every figure here comes from historical federal filings, not a prediction of any future flight, and nothing here is professional travel advice.