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

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

Trump has long touted tariffs as a lucrative revenue source, saying on Tuesday that "the big money" would start to flow in after he imposes higher "reciprocal" tariffs on U.S. trading partners on August 1. Trump 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 on a gross basis and $108 billion 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 federal government, behind individual withheld receipts at $2.683 trillion for the fiscal year, non-withheld individual receipts at $965 billion and corporate taxes at $392 billion.

In the space of roughly four months, tariffs as a share of federal revenue have more than doubled to around 5% from about 2% historically.

The 2025 fiscal year runs from October 1, 2024 to September 30, 2025.

The June budget surplus represented a turnaround from the $71 billion deficit in June 2024. The new tariff-related revenue helped boost total budget receipts last month by 13%, or $60 billion, to $526 billion, a record for that month, the Treasury said. Outlays in June fell 7%, or $38 billion, to $499 billion.

But adjusting for calendar shifts of some revenue and benefit payments, it said there would have been a budget deficit of $70 billion in June along with a year-ago adjusted deficit of $143 billion.

The overall year-to-date deficit, however, increased 5%, or $64 billion, to $1.337 trillion, as outlays for health care programs, Social Security retirement benefits, defense spending and interest on the national debt increased, the Treasury said.

Receipts for the first nine months of the fiscal year rose 7%, or $254 billion, to a record $4.008 trillion, while outlays grew 6%, or $318 billion, to a record $5.346 trillion.

The Treasury's interest costs on the growing national debt continued to grow, reaching $921 billion for the first nine months of the fiscal year, up 6%, or $53 billion, from the year-ago period. 

But the Treasury's weighted average interest rate largely had stabilized at 3.3% at the end of June, up two basis points from a year ago, a Treasury official said.

BIGGER FLOW

Treasury Secretary Scott Bessent earlier this week suggested a steeper ramp-up in tariff collections, telling a cabinet meeting that calendar-year 2025 collections could grow to $300 billion by the end of December. 

At the June run rate, gross customs collections would hit $276.5 billion in six months' time, which means reaching Bessent's target would require some increases.

Bessent added that the CBO has estimated tariff-related income will total about $2.8 trillion over 10 years, "which we think is probably low."

Trump has set a new August 1 deadline for higher "reciprocal" tariff rates to kick in on nearly all U.S. trading partners, with room for negotiations with some countries in the next three weeks for deals to lower them.

Since those remarks on Tuesday, the U.S. president has put his tariff assault into overdrive, announcing 50% levies on copper imports and goods from Brazil and a 35% tariff on Canadian goods, all due to start on August 1.

The Trump administration is preparing more sector-based tariffs on semiconductors and pharmaceuticals.