A day of the week calculator is a perpetual calendar in one box: give it any date and it tells you the weekday it falls on, plus the day of the year, the ISO week number, and how far it is from today. Use it to find the day you were born, check which day a holiday or deadline lands on, or settle a "what day was that?" debate — for any year, past or future, in the Gregorian calendar.
Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: Gregorian-calendar and ISO 8601 week rules, recomputed in code.
What the calculator reports
The weekday comes straight from the Gregorian calendar. The day-of-year number counts from 1 January, reaching 366 in a leap year. The ISO 8601 week number is the one businesses use for planning: weeks start on Monday and week 1 is the week holding the year's first Thursday — which is why a date like 1 January can belong to week 52 of the previous year. The "from today" figure compares against your device's current date.
Worked example — 26 June 2026 and friends
Scenario: look up 26 June 2026, then a few landmark dates.
26 June 2026 is a Friday, the 177th day of the year, in ISO week 26 — right at the year's midpoint. The Apollo 11 Moon landing on 20 July 1969 was a Sunday. And 1 January 2000 lands in ISO week 52 — a perfect illustration of the ISO quirk, where an early-January date belongs to the last week of the prior year because that week's Thursday fell in December.
Frequently Asked Questions
Enter your birth date for the weekday. E.g. 20 Jul 1969 (Moon landing) was a Sunday.
Position in the year from 1 Jan = 1. 26 Jun 2026 is day 177; 25 Dec is day 359.
Monday-start weeks 1–52/53; week 1 holds the first Thursday (4 Jan).
If 1 Jan is Fri/Sat/Sun it falls in the prior year's last week. 1 Jan 2000 = wk 52.
Whole dates only — weekday is the same everywhere, no time-zone adjustment.