Seasonal Index <No Password>

= Actual ÷ Seasonal Index.

[ \textSeasonal Ratio = \frac\textActual Value\textCentered Moving Average ] seasonal index

This ratio represents the combined effect of seasonality and random noise. Group all ratios by month (or quarter, etc.) and calculate the median or mean (median is less sensitive to outliers). Step 4: Adjust So That Average = 1 If the average of your raw seasonal indices is not exactly 1, adjust them: = Actual ÷ Seasonal Index

(We’ll skip full arithmetic for brevity – but you’d smooth the data.) seasonal index