Day Number Calculator
Find the day-of-year number (1–366), the ISO week, and the weekday for any date.
Reviewed by the CalcCafe editorial team · Last updated 1 July 2026 · How we test our tools
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.
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Sources & references
These tools follow our methodology and provide educational estimates only — verify important figures with a qualified professional.