What day does a calendar year begin?

A calendar year begins on January 1 because it is the date that marks the start of a new year in the Gregorian calendar, which is the most widely used civil calendar in the world today. This system divides the year into 12 months, with January being the first month. The significance of January 1 as New Year's Day is rooted in historical traditions and conventions, making it a universally recognized starting point for tracking time over the course of a year.

The other options do not represent the start of the calendar year; December 31 is recognized as the last day of the year, while July 1 and July 31 occur roughly halfway through the year. Hence, only January 1 serves as the correct answer when determining the beginning of a calendar year.