Shipping peak season: when and why US imports surge

Shipping peak season is the late-summer-into-fall stretch when US container imports run at their heaviest, traditionally August through October. The driver is the retail calendar. Goods sold in the fourth-quarter holiday rush have to be made, shipped, landed and trucked to shelves weeks ahead, so importers front-load the orders in the third quarter. That pull-forward is what turns the late-summer months into the busiest window on the import calendar.

See it in the multi-year shape

The chart above is monthly loaded imports across the nine US container ports this site tracks, back to January 2019. Loaded imports are the inbound boxes with cargo in them, the import-demand read. Read across the years and the shape repeats: a dip in late winter, a build through summer, a plateau into the fall. Line up this year against the same months last year to see whether a peak is early, late or on time. The line ends at the last month every tracked port has published, because the port figures land through BTS weeks after the month closes.

Peak season year by year

Two readings come out of the table. First, the August-to-October block is real: an even spread would put 25% of a year's imports in any three months, and those three carried more than that in every year from 2019 to 2025 except 2022. Second, the single heaviest month moves around. It landed in August, September or October in 2020, 2023 and 2024, in July in 2019 and 2025, and in May in 2021 and 2022. A peak season is a window of heavy months, and in several years the window opened early.

A worked example: 2024

2024 is the textbook year. Loaded imports at the nine tracked ports were 2,214,564 TEU in August, the year's heaviest month, then 2,168,038 in September and 2,142,535 in October. Those three months add up to 6,525,137 TEU of the year's 24,291,498, or 26.9%. An even quarter of the year would have been about 6,072,900 TEU, so peak season carried roughly 452,000 TEU more than its even share. Put per month, August to October averaged 2,175,046 TEU against 1,974,040 for the other nine months, 10.2% heavier.

2025 shows the other shape. July was the heaviest month at 2,283,488 TEU, and August to October ran only 3.3% above the rest of the year. In 2026, through June (the last month all nine ports have published as of mid-October), May was the heaviest month at 2,138,421 TEU, with June close behind at 2,128,148.

Why the surge lands when it does

Work the holiday timeline backward. A product on a store shelf in November left an Asian factory two to eight weeks earlier depending on the route, and it was ordered weeks before that. To hit an October floor-set date a box generally has to ship by August, which is why import volume swells from midsummer. Back-to-school buying adds an earlier bump, and the two demand waves overlap into one long push through the third quarter. The boxes have to move before the quarter they serve, not during it.

The factory calendar on the other end

The origin calendar shapes the year too. Chinese factories close for the Lunar New Year, which falls in late January or February, and production slows for weeks around it. Importers who need goods in the first quarter often pull those orders forward ahead of the shutdown, creating a second, smaller rush before the holiday one. The trough after the shutdown shows in the data: the lightest month of the year for the tracked ports was February or March in five of the seven full years from 2019 to 2025.

Why the peak has been moving earlier

The classic August-to-October peak has drifted earlier in recent years as importers pull cargo forward to get ahead of labor uncertainty, tariff deadlines and the risk of congestion. In 2021 and 2022, with the ports already backed up, the heaviest month came in May. The pattern is a tendency, not a fixed schedule, and the monthly volume data is where you see which shape a given year took.

What the ship queue shows in peak season

The faster signal is the count of container ships waiting for a berth, which updates weekly while the volume figures land a month or more after the fact.

The national count of container ships awaiting berth was 7 ships (reading of Oct 13, 2026).

More boxes do not always mean a longer line. In this site's weekly readings, the national queue averaged more ships in August to October than in the rest of the year in 2023 (22.1 against 16.7) and 2024 (19.4 against 16.7), but fewer in 2025 (11.9 against 15.9). In 2021 and 2022 the backlog was large all year, and the August-to-October readings ran below the year's other weeks on record. A terminal with slack absorbs a normal peak without a queue; a queue forms when arrivals outrun berths, yard space, trucks and rail, which what causes port congestion covers cause by cause.

The Dwell shows the seasonal pattern in the volume data, dated to the month, and the queue weekly. It does not forecast how big a given peak will be. For how to read a fresh monthly release, see reading the monthly TEU release.