Day Number Calculator
Find the day-of-year number (1–366), the ISO week, and the weekday for any date.
Day number (day of year)
ISO week
Weekday
How it works
The tool counts the days from 1 January of the date's year to the date itself.
Everything is computed locally in your browser — nothing is uploaded.
Frequently asked questions
What is a day number?
The day number, or ordinal date, is the position of a date within its year — 1 for 1 January, up to 365 or 366 for 31 December.