Day of Year Calculator

How to use

1. 1Open the calculator and the top panel shows today's day of year, the days remaining this year, the percentage of the year elapsed, and a progress bar.
2. 2Keep Date to day number selected to find the day of the year for any date: pick a date or type YYYY-MM-DD and read the day number, ISO ordinal date, and YYDDD code.
3. 3Switch to Day number to date to go the other way: enter a year and a day number from 1 to 365 or 366 and the matching calendar date and weekday appear.
4. 4Check the days remaining and year elapsed figures to see how far through the year a date falls, useful for deadlines, quotas, and date codes.
5. 5Use the Copy buttons to grab just the day number, the calendar date, or a full summary block, then press Use today to reset both modes to the current date.

About this tool

Day of Year Calculator turns a calendar date into its ordinal day number, the position of that date within its year counting from 1 on January 1. December 31 lands on day 365 in a common year and day 366 in a leap year, and the tool handles the leap-year rule for you, so February 29 only resolves in years that actually have it. Use Date to day number to pick any date and read back its day of year, the number of days remaining until December 31, the percentage of the year that has elapsed, and the ISO 8601 ordinal form written as YYYY-DDD. Use Day number to date to go the other way: type a year and a day number from 1 to 365 or 366 and get the exact calendar date, its weekday, and the long form. The header panel always shows today's day of year, how many days are left in the current year, a progress bar of the year so far, and today's ordinal date, so you can answer what day of the year is it at a glance. The tool also prints the YYDDD and YYYYDDD ordinal date strings that manufacturing date codes, egg cartons, aircraft part stamps, and mainframe systems use, where a five-digit code such as 26172 means the 172nd day of 2026. These ordinal forms are sometimes loosely called a Julian date, which is a different thing from the astronomical Julian Day Number counted continuously from 4713 BCE; this calculator produces the civil day-of-year ordinal, matching spreadsheet day-of-year formulas, the strftime %j directive, Python timetuple tm_yday, and PostgreSQL doy. Every value can be copied, including a full summary block for pasting into a report or a label template. All of the math runs in UTC inside your browser, so the day number never shifts because of your local timezone and nothing you type is uploaded, logged, or stored.

Free to use. Works in your browser. No signup, no login.