How to compute SPI on 1-month time scale and 5-month time scale ?

You can calculate n-month SPI easily. You would follow these steps:

  1. Sort your monthly data in an Excel file
  2. Calculate moving average based on: Simple Moving Average Formula or the below video.
  3. Calculate SPI by the moving average data as monthly data

Notice: Monthly SPI is equal to monthly SPI so you can calculate monthly SPI and get it 1-month SPI

Notice: You can use one of our tools(MDM, RDIT, or DMAP) for this calculation or you can calculate it manually in Excel. Visit this page: How to calculate standard precipitation index in excel?


Simple Moving Average Formula