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Finding BLS Seasonal Factors for CPI Adjustment

Article Quant Q&A · Author: Thomas David
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Summary

The document addresses how to obtain a single seasonal adjustment factor for a consumer price index series when the downloaded BLS seasonal-factors workbook is organized by expenditure category. The response points to a separate BLS publication, the revised seasonal indexes file, which already provides seasonal factors for the past year. For the goal of adjusting CPI observations, the suggested approach is to use that series directly rather than combine category-level factors.

The answer is brief and does not explain how the agency constructs the revised indexes, how to apply them to CPI levels, or how to handle data revisions outside the period covered. It notes that recalculating factors from expenditure components may still be appropriate if that reconstruction is itself the research objective. The discussion therefore offers a data-source clarification, not a seasonal-adjustment method or an analysis of trading implications.

Key ideas

  • The BLS revised seasonal indexes file provides seasonal factors for the past year.
  • The response recommends using the published aggregate indexes instead of deriving one factor from expenditure-level data.
  • Recalculation from expenditure components is relevant only if reconstructing the factors is the objective.
  • The document does not explain the adjustment procedure or the treatment of revisions beyond the stated coverage.

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# Extracting seasonal factor of CPI from BLS


# Extracting seasonal factor of CPI from BLS












I want to extract the seasonal factor to get the seasonal adjustments of each CPI fixing in order to create a seasonally-adjusted CPI series.

The BLS publishes the seasonal-factor on their website at this link: https://www.bls.gov/web/cpi.supp.toc.htm

However, when you download the cpi-seasonal-factors.xlsx file, you get the seasonal factor broken up by expenditure. How do I use this data to construct a singular number for each month so I can adjust CPI?

## Answer by Thomas David (score 1)

https://quant.stackexchange.com/a/83898

You have to download the cpi-revised-seasonal-indexes Excel file available on the BLS website. That includes the seasonal factor for the past year. There is no need to recalculate the seasonal factor from the expenditures - unless that is the goal.

Shown in full with attribution under the source's licence. Licence: CC BY-SA 4.0 (Stack Exchange)

This summary was written by Stratmill's research agent from the original; it is not a copy of the source.