Financial reports are based on a company's fiscal year instead of the calendar year. A fiscal year, used for accounting purposes, can start on any day of a calendar year, and usually straddles two consecutive calendar years. For example, Apple's fiscal year 2021 (or FY 2021) ran from September 27, 2020 to September 25, 2021. Therefore, its financial report for the first quarter of FY 2021, i.e. 2021Q1, was as of December 26, 2020.