Day of Year Calculator

Name: Day of Year Calculator
Author: Jürgen Kummer

Calculates for any date the number for the day of the year. The days are counted continuously from January 1. to December 31. The year is only relevant in so far as it is a leap year or not.

Examples: in a normal year, August 1. is the 213. day of the year, in a leap year it is the 214. February 10th, however, is always the 41st day of the year, regardless of whether it is a leap year or not.

Our calendar, which starts in January and ends in December, goes back to the ancient Romans. More precisely, to the calendar reform of 153 BC, when the Roman consuls began their official duties on January 1st instead of March 1st as before. The Romans wanted to take action against rebellions by the Hispanic Celts and therefore wanted to elect a new consul as quickly as possible. The calendar reform under Julius Caesar finally put January and February at the beginning of the year. The fact that our year begins in January is therefore more or less a historical coincidence. However, January 1st is close to the winter solstice, which is on December 21st or 22nd and which in many cultures represents a new beginning, as the days become longer again from this point onwards.
Up to February 28th, the 59th day of the year, the numbering of the days is the same in every year. The 60th day of the year is March 1st in a normal year, and February 29th in a leap year. The last day of the year, December 31st, is the 365th day in a normal year and the 366th day in a leap year. In a normal year, the exact midpoint of the year is on July 2nd at 12:00 noon. July 2nd is the 183rd day of the year, with 182 days before and 182 days after. In a leap year, the exact midpoint of the year is at midnight between July 1st and 2nd, the 183rd and 184th days of the year.

Last updated on 12/20/2025. Author: Jürgen Kummer

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