Need to know whether a wedding date falls on a Saturday, or which weekday Independence Day lands on next year?
About this calculator
Need to know whether a wedding date falls on a Saturday, or which weekday Independence Day lands on next year? This calculator names the weekday for any Gregorian date and adds context: day-of-year position, ISO week number, and how many calendar weeks have passed since 1 January 1970.
Pick a date from the built-in calendar control, or switch to manual entry and type day, month, and year — useful for historical dates or when you already know the numbers from a document. Invalid combinations like 31 February are rejected.
Day-of-year helps with seasonal planning (day 180 is roughly mid-year). ISO week numbers appear on payroll systems and project Gantt charts. Weeks since epoch is a fun anchor for comparing how far apart two dates sit on the calendar timeline. Pair with the [[date]] calculator for adding or subtracting days, the [[age]] calculator for birth-date math, and the [[workdays]] calculator when you need business days instead of weekdays.
Common uses
- Event planning — confirm Saturday vs Sunday for a venue booking
- Historical lookup — weekday for a birth or marriage certificate date
- Payroll and ISO week alignment for weekly pay cycles
- School and exam timetables tied to day-of-year counts
- Trivia and genealogy — day-of-year and epoch week facts
Frequently asked questions
What weekday was 15 August 1947?
Switch to manual entry, type day 15, month 8, year 1947. The calculator returns Friday — India
What is day of year?
Day of year counts from 1 January. 1 January is day 1; 31 December is day 365 (366 in a leap year). Useful for agriculture, astronomy, and fiscal calendars that track progress through the year.
How is ISO week number defined?
ISO 8601 sets week 1 as the week containing the first Thursday of January. Weeks run Monday to Sunday. The same date can fall in week 52 of one year and week 1 of the next near year boundaries.
What does weeks since epoch mean?
It counts whole calendar weeks from 1 January 1970 (the Unix epoch date) to your chosen date. It is a rough timeline measure — not the same as Unix timestamp seconds, but handy for comparing date spacing.
Does the calculator handle leap years?
Yes. February 29 is accepted in leap years and rejected in non-leap years. Day-of-year totals use 366 days for leap years and 365 otherwise.