Free Seasonal Adjustment Calculator
Remove seasonal effects from time-series data by dividing the observed value by its seasonal index.
Seasonally Adjusted Value
120.0000
Seasonal Effect30.0000
Seasonal Effect (%)25.0000
Seasonally Adjusted Value vs Observed Value
How to Seasonally Adjust Data
Formula
Adjusted Value = Observed Value / Seasonal Index
Seasonal adjustment removes predictable seasonal patterns from data, revealing the underlying trend. A seasonal index above 1 means the season inflates the value; below 1 means it deflates it. Dividing by the index normalizes the value as if there were no seasonal effect.
Example Calculation
December sales are $150 with a seasonal index of 1.25 (holiday boost).
- 01Adjusted = 150 / 1.25 = 120
- 02Seasonal effect = 150 - 120 = 30
- 03The seasonal boost accounts for $30 (25%) of the observed value
- 04The underlying (de-seasonalized) value is $120
Frequently Asked Questions
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