The day of year is the ordinal position of a date inside its calendar year. January 1 is day 1, January 31 is day 31, and December 31 is day 365 in a normal year or day 366 in a leap year. This format appears in scientific datasets, manufacturing schedules, satellite and weather records, software releases, accounting workflows, and logs where a compact year-plus-day value is more convenient than a month-and-day label.
GeoTimeTools’s day of year calculator accepts a date and returns its ordinal day, the number of days remaining, the weekday, and whether the year is a leap year. The calculation uses the calendar date in UTC rather than the visitor’s local time, so midnight differences between devices do not change the answer. It is intentionally small: choose the date, read the day number, and copy it into the system or document that needs it.
This page is also helpful for questions such as “what day of 365 is today?” or “what is the day number for this date?” If you need a week number, use the companion Week Number Calculator. If you need the number of working days between two dates, use the Business Days Calculator instead. Those related tools share the same clean workflow but keep their calculations distinct.
Leap years change the final stretch
A leap year has 366 days because February contains 29 days. The calculator uses the Gregorian rule: years divisible by four are leap years, except century years that are not divisible by 400. That keeps dates such as 1900 and 2000 correct.
Day number versus week number
The day of year counts from January 1 one date at a time. A week number groups dates into seven-day periods and can follow ISO or US conventions. Use the format that matches the system receiving your value.