Jakarta. Rupiah strengthened at the start of the week on Monday as markets weighed geopolitical developments, fresh US tariff measures and a landmark Supreme Court ruling in Washington.

The Indonesian currency closed 86 points higher against the US dollar at Rp 16,802 in afternoon trading, from the previous close of Rp 16,888. Earlier in the session, the rupiah had gained as much as 90 points.

Ibrahim Assuaibi, Director of Traze Andalan Futures, projected continued volatility for Tuesday. “For tomorrow’s trading, the rupiah is expected to fluctuate but close stronger in the range of Rp 16,770 to Rp 16,800,” Ibrahim said in a written statement on Monday. He noted that the rupiah firmed as investors monitored escalating geopolitical tensions between the United States and Iran in the Middle East.

“The market continues to observe the third round of nuclear talks between the US and Iran on Thursday in Geneva, raising hopes that tensions could ease,” he said.

The currency also advanced despite US President Donald Trump announcing a 10% tariff on global imports for 150 days under Section 122 of US trade law, following a Supreme Court ruling that overturned the previous tariff regime. Trump later raised the tariff to 15%, the maximum allowed under the law, heightening concerns over potential retaliation and disruptions to global supply chains.

As background, on Friday local time, the US Supreme Court voted 6–3 that Trump does not have the authority to impose global tariffs under the International Emergency Economic Powers Act (IEEPA).

Trump called the ruling “very disappointing” and accused the court of being influenced by “foreign interests.” He stressed that all national security tariffs remain in effect and that the ruling specifically concerns the use of IEEPA-based tariffs.

“Uncertainty regarding the duration and scope of the tariffs, as well as potential legal and congressional challenges, is adding to market volatility,” Ibrahim said, adding that such conditions could influence the rupiah’s movement going forward.

Lukman Leong, a currency analyst at Doo Financial Futures, said the real impact of the ruling remains unclear.

“The real impact is still uncertain because Trump is insisting on moving forward, although at least this is a positive decision for the world,” Lukman said.

The rupiah also drew support from weaker US economic data. US fourth-quarter 2025 gross domestic product growth slowed to 1.4%, far below the 3% expectation and down from 4.4% previously, partly due to a 43-day government shutdown.

“The majority was caused by the government shutdown and weakened purchasing power due to tariffs,” Lukman said.