How the weekday is determined
The day of the week is computed using the Gregorian calendar algorithm. Every date maps to an exact day from Sunday through Saturday.
The tool also computes the ordinal day of the year (1 to 366) and the ISO 8601 week number commonly used in logistics and financial accounting.
Worked example
For 7 November 2026:
The calculator establishes that this date falls on a Saturday (a weekend day). It is day 311 of the year in ISO week 45, in a common year of 365 days.
Inputs for the date of week calculator
Calendar date
The specific calendar date you wish to inspect.
CALCULATOR QUESTIONS
Date of week calculator questions
Can I find what day of the week I was born on?
Yes, enter your date of birth into the input box and the calculator will instantly display the exact day of the week.
What is an ISO week number?
ISO 8601 defines week 1 of the year as the week containing the first Thursday of January, with weeks starting on Monday.