U.S. customs duty collections jumped again in June as U.S. President Donald Trump's tariffs gained steam, topping $100 billion US for the first time during a fiscal year and helping to produce a surprise $27-billion US budget surplus for the month, the U.S. Treasury Department reported on Friday.

The budget data showed that tariffs are starting to build into a significant revenue contributor for the U.S. government, with customs duties in June hitting new records, nearly quadrupling to $27.2 billion US on a gross basis and $26.6 billion US on a net basis after refunds.

Trump has long touted tariffs as a lucrative revenue source, saying Tuesday that "the big money" would start to flow in after he imposes higher "reciprocal" tariffs on U.S. trading partners on Aug. 1. The U.S. president disagrees with economists who consistently say those taxes are paid by U.S. consumers and importers.

For the first nine months of fiscal 2025, the customs take reached records of $113.3 billion US on a gross basis and $108 billion US on a net basis, nearly double the prior-year collections.

Based on those results, tariffs have now grown into the fourth-largest revenue source for the U.S. government.

In the space of roughly four months, tariffs as a share of federal revenue have more than doubled, to around five per cent from about two per cent historically.

The 2025 fiscal year runs from Oct. 1, 2024, to Sept. 30, 2025.