ISM® Makes Annual Adjustments to Seasonal Factors for ISM® Manufacturing PMI® and Diffusion Indexes and ISM® Services PMI® and Diffusion Indexes

TEMPE, Ariz., Jan. 29, 2026 /PRNewswire/ -- Based on input from an independent expert, Institute for Supply Management® (ISM®) recently announced the completion of its annual adjustments to the seasonal factors used in the monthly ISM® Manufacturing PMI® Report and the monthly ISM® Services PMI® Report. Purchasing managers and economists who track these indexes will note that changes are effective with the January 2026 ISM® Manufacturing PMI®, which is scheduled to be released on February 2, 2026, and the January 2026 ISM® Services PMI®, which will be released on February 4, 2026.

Seasonal adjustment factors are used to allow for the effects of repetitive intra-year variations resulting primarily from normal differences in weather conditions, various institutional arrangements, and differences attributable to non-movable holidays. It is standard practice to project the seasonal adjustment factors used to calculate the indexes one year ahead (2026).

As in previous years, the X-13-ARIMA program was used to develop the revisions to the Manufacturing and Services indexes for January 2023 through December 2025, as well as the 2026 projected seasonal factors. The 2026 seasonal factors will be recomputed when the actual data are known in early 2027. Projected seasonal factors for 2026 are shown below.

2026 Seasonal Adjustment Factors for ISM® Manufacturing Indexes

To compute the Manufacturing PMI® Index and Subindexes:

1)  Calculate the unadjusted diffusion index for New Orders, Production, Employment and Inventories (percent higher plus one half of the percent same or unchanged) to one decimal place and Supplier Deliveries (percent slower plus one half of the percent same or unchanged) to one decimal place.

2)  Divide each unadjusted diffusion index by its seasonal factor and round each quotient to one decimal place.

3)  Add all five quotients (index numbers) together and divide by five to arrive at the seasonally adjusted Manufacturing PMI Index.

4)  For each of the five other subindexes, calculate the diffusion index by adding together the percent higher and one half of the percent same or unchanged, then rounding that sum to one decimal place.

2026 Seasonal Adjustment Factors for ISM® Services PMI® Indexes

To compute the Services PMI® Index and Subindexes:

1)  Calculate the unadjusted diffusion index for New Orders, Business Activity, and Employment (percent higher plus one half of the percent same or unchanged) to one decimal place and Supplier Deliveries (percent slower plus one half of the percent same or unchanged) to one decimal place.

2)  Divide each unadjusted diffusion index by its seasonal factor and round each quotient to one decimal place.

3)  Add all four quotients (index numbers) together and divide by four to arrive at the seasonally adjusted Services PMI index.

4)  For each of the six other subindexes, calculate the diffusion index by adding together the percent higher and one half of the percent same or unchanged, then rounding that sum to one decimal place.

Please note that differences in rounding practices may result in computed values that differ from published values.

About ISM® PMI® Reports 
The ISM® PMI® Reports are considered by many economists to be the most reliable near-term economic barometer available. It is reviewed regularly by top government agencies and economic and business leaders for its timely, accurate information. The Manufacturing and Services ISM® PMI® Reports are published monthly by Institute for Supply Management®. Each month, both reports are compiled from responses to questions asked of purchasing and supply executives across the country and reflects change, if any, in the current month compared to previous months.

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