Calendar Year

What Does Calendar Year Mean?
The one-year period that begins on January 1 and ends on December 31, based on the commonly used Gregorian calendar. For individual and corporate taxation purposes, a calendar year will generally comprise all of the year's financial information used to calculate income tax payable.

Investopedia explains Calendar Year
Most individuals and many companies use the calendar year as their fiscal year, or the one-year period on which their payable taxes are calculated. However, some companies choose to report their taxes based on a fiscal year (e.g. starting on April 1 and ending on March 31) to better conform to seasonality patterns or other accounting concerns applicable to their businesses.