A comparative income statement will consist of two or three columns of amounts appearing to the right of the account titles or descriptions. For example, the income statement for the year 2020 will report the amounts for each of the years 2020, 2019, and 2018. As a courtesy to the reader, the amounts from the most recent period are in the column closest to the titles. The older amounts are deemed to be less significant and thus appear furthest from the titles.
A comparative income statement gives the reader a frame of reference for comparing the current year amounts.