Calculate the grand mean of all data points across all periods.
Seasonal indices help you uncover repeating patterns in your data — whether it’s sales, web traffic, or demand. Here’s how to calculate them step by step: how to find seasonal index
Want to go deeper? Use Excel, Python ( statsmodels ), or R for advanced decomposition (additive or multiplicative). Calculate the grand mean of all data points
Here’s a clear, professional post you can use for LinkedIn, a blog, or a social media update: Python ( statsmodels )