According to private sector indicators, inflation in the U.S. rebounded in September, providing further evidence that tariffs have pushed certain prices higher amid the absence of official government metrics.

PriceStats, which bases its data on products sold by online retailers, reported strong price increases for goods such as household appliances and furniture, pushing the annual inflation rate to its highest level in two years. Another metric from OpenBrand indicated the strongest monthly price growth since June, primarily driven by personal care products and communication devices.

Despite significant price increases in September, particularly for imported goods, economists believe inflation will begin to ease next year, largely dependent on service costs. Unlike private sector reports, service costs are more comprehensively reflected in the CPI data, which has been delayed to later this month due to the government shutdown.

Ralph McLaughlin, the chief economist at OpenBrand, described the trend as akin to a plane descending, with tariffs causing some "turbulence." He noted that the cancellation of the “de minimis exemption” in August may have pushed up last month’s inflation, a provision that previously allowed imports valued at up to $800 to be exempt from tariffs.

"Tariffs are like minor turbulence, causing the plane to jolt upward, but overall, the plane is still on a downward trajectory," McLaughlin explained. "This metaphor represents our view on how tariffs will impact prices."

Analysts Anna Wong and Alex Tanzi pointed out that their tracking of millions of prices over the past few months suggests that September's CPI might be moderate enough to allow the Federal Open Market Committee (FOMC) to lower interest rates comfortably in October.

Unlike the job market, alternative measures of inflation are relatively sparse, as noted by Fed Chairman Jerome Powell at a meeting on Tuesday. This scarcity is attributable to the labor-intensive nature of collecting price quotes. The Bureau of Labor Statistics (BLS) typically deploys hundreds of data collectors across the country each month to gather prices for about 80,000 goods and services, which requires visits to businesses ranging from grocery stores to medical offices.

For the private sector, this is also a challenging task, and the process goes well beyond data collection, according to Alberto Cavallo. His Billion Prices Project laid the groundwork for PriceStats.

"You have to make sure the data is categorized correctly. Then you must know what to include and exclude, and decide how to handle missing data and adjust for seasonal and other patterns," Cavallo said. "So it's no easy feat."

During the government shutdown, much of the BLS's operations, including this process, has been halted. However, the agency has been instructed to recall some employees to compile September's CPI so that the Social Security Administration can adjust its annual cost of living. The report is now scheduled for release on October 24.

In the meantime, investors can rely on private sector data for preliminary insights. However, these indicators often do not capture service prices related to dining out and travel. OpenBrand's report covers durable and personal goods, categorized into appliances and cosmetics, among others.

PriceStats similarly focuses on goods and does not track housing inflation. Platforms like Zillow Group Inc. and Realtor.com have their own housing price metrics, but the BLS employs a unique calculation method for housing costs, with its broader CPI housing category also including hotel accommodations.

Other reports hint at certain aspects of inflation but do not reflect the extent of price increases. A service price index from the Institute for Supply Management (ISM) rose to one of its highest levels in nearly three years last month; a small business survey in September found that a net 31% of owners plan to raise prices in the next three months, one of the highest proportions since early 2024.

"We are starting to become a bit more concerned about this trend," said Michael Metcalfe, head of macro strategy at State Street Global Markets, which is responsible for analyzing and distributing PriceStats' data. "We are entering a period when prices should typically be quite subdued, but the data from PriceStats does not currently indicate that normal softness."

It remains unclear what sort of discounts retailers will be able to offer consumers this holiday shopping season. President Trump’s latest tariffs on lumber and wood products only took effect on Tuesday, but the "Tariff Tracker" from Harvard Business School's pricing lab, led by Cavallo, shows that the statement made on September 29 has already triggered price increases for domestic and imported goods.

Cavallo indicated that while there is a rapid reaction to new developments in trade, the broader trend shows that the impact on consumer prices is more stable.

"I think many people expect a large change that would significantly push inflation up. But that is not the case," he said. "It’s more of a gradual transmission that is slowly applying upward pressure on prices."