Inflation cooled unexpectedly sharply in March, a welcome development given the uncertainties surrounding President Trump’s global tariffs that are widely expected to stoke price pressures while also denting growth.

The Consumer Price Index climbed 2.4 percent last month from a year earlier, a far slower pace than February’s 2.8 percent increase and the lowest annual rate since September. Over the course of the month, prices fell 0.1 percent.

A gauge tracking underlying “core” inflation, which strips out volatile food and energy items, slipped to 2.8 percent in March, following a 0.1 percent monthly increase.

The report, which was released by the Bureau of Labor Statistics on Thursday and significantly undershot economists’ expectations, covers a period before the bulk of Mr. Trump’s tariffs were put in place. In recent days, the president’s plans have changed dramatically, culminating in the administration on Wednesday announcing a 90-day pause on punishing levies that had been put in place on April 2.

Mr. Trump’s decision to pause came as global financial markets wobbled and started to flash warning signs about investors’ appetite for U.S. assets. Goods coming into the country from most countries will now face a 10 percent tariff, while Chinese imports will face a 125 percent charge, following Beijing’s decision to retaliate against U.S. products.

Mr. Trump’s pivot significantly eased worries about the extent of the economic damage stemming from his administration’s trade policies. But economists warn that the tariffs in place will still prove costly, leading not only to slower growth but higher inflation.

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