Based on input from an independent expert, Institute for Supply Management (ISM) recently completed its annual adjustments to the seasonal factors used in the monthly ISM Manufacturing PMI Report and the monthly ISM Services PMI Report.
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
| New Orders |
Production |
Employment |
Inventories |
|
| Jan-2026 | 0.997 | 0.985 | 0.991 | 0.992 |
| Feb-2026 | 1.053 | 1.020 | 1.008 | 1.026 |
| Mar-2026 | 1.071 | 1.014 | 1.019 | 1.039 |
| Apr-2026 | 1.075 | 1.080 | 1.050 | 0.993 |
| May-2026 | 1.030 | 1.024 | 1.046 | 1.018 |
| Jun-2026 | 0.974 | 1.016 | 1.031 | 0.985 |
| Jul-2026 | 0.983 | 0.981 | 0.976 | 0.983 |
| Aug-2026 | 0.963 | 0.971 | 0.980 | 1.017 |
| Sep-2026 | 0.977 | 1.002 | 0.957 | 1.013 |
| Oct-2026 | 0.968 | 0.984 | 0.989 | 0.986 |
| Nov-2026 | 0.961 | 0.978 | 0.973 | 0.978 |
| Dec-2026 | 0.948 | 0.936 | 0.978 | 0.960 |
To compute the Manufacturing PMI Index and Subindexes:
- 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.
- Divide each unadjusted diffusion index by its seasonal factor and round each quotient to one decimal place.
- Add all five quotients (index numbers) together and divide by five to arrive at the seasonally adjusted manufacturing PMI Index.
- 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
| Business Activity | New Orders | Employment | Prices | |
| Jan-2026 | 0.939 | 0.961 | 0.970 | 0.987 |
| Feb-2026 | 0.967 | 1.015 | 0.976 | 1.010 |
| Mar-2026 | 1.004 | 0.985 | 1.021 | 1.023 |
| Apr-2026 | 1.057 | 1.052 | 1.002 | 1.056 |
| May-2026 | 1.008 | 1.008 | 1.007 | 1.047 |
| Jun-2026 | 0.991 | 0.988 | 1.027 | 1.012 |
| Jul-2026 | 1.027 | 0.991 | 1.007 | 1.007 |
| Aug-2026 | 0.985 | 0.989 | 0.992 | 0.982 |
| Sep-2026 | 1.049 | 1.012 | 1.002 | 1.001 |
| Oct-2026 | 1.017 | 1.049 | 1.004 | 0.990 |
| Nov-2026 | 0.979 | 0.996 | 0.995 | 0.957 |
| Dec-2026 | 0.983 | 0.965 | 0.996 | 0.928 |
To compute the Services PMI Index and Subindexes:
- 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.
- Divide each unadjusted diffusion index by its seasonal factor and round each quotient to one decimal place.
- Add all four quotients (index numbers) together and divide by four to arrive at the seasonally adjusted services PMI index.
- 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.
Note that differences in rounding practices may result in computed values that differ from published values.
