Seasonal Index Free May 2026

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

1. What Is a Seasonal Index? A seasonal index (also called a seasonal component or seasonal factor) is a numerical value that quantifies how a particular time period (e.g., a month, quarter, or week) compares to the average period in a seasonal cycle. It is used to measure and remove seasonal variation – predictable, recurring fluctuations that happen within a fixed period (usually one year).

[ \textActual = \textTrend \times \textSeasonal \times \textIrregular ] seasonal index

| Year | Q1 | Q2 | Q3 | Q4 | |------|----|----|----|----| | 2022 | 80 | 120 | 100 | 140 | | 2023 | 90 | 130 | 110 | 150 |

(We’ll skip full arithmetic for brevity – but you’d smooth the data.) It is used to measure and remove seasonal

[ \textAdjusted Index_i = \frac\textRaw Index_i\textMean of Raw Indices ]

After dividing actual by the seasonal index, you get , which reveals the true trend and cycle. seasonal index

= Actual ÷ Seasonal Index.