How far back can I check a date?

The tool uses the JavaScript Date object, which supports dates from the year 100 onward. For dates before the Gregorian calendar reform (1582 in most countries), the tool still calculates the day of the week using the proleptic Gregorian calendar.

What is the ISO week number?

The ISO week number is defined by ISO 8601. Week 1 is the week containing the year's first Thursday. This means January 1st may fall in week 52 or 53 of the previous year, and late December dates may belong to week 1 of the next year.

What does 'day of the year' mean?

It's the ordinal count of the day from January 1st. January 1st is day 1, January 2nd is day 2, and so on. In a leap year, December 31st is day 366; in a non-leap year, it's day 365.

Can I find all occurrences of a specific weekday in a month?

The current tool shows the day of the week for a single date. To find all Fridays in a given month, you would need to check each date individually. A future update may add this feature.

How does the calculator handle leap years?

The tool correctly identifies leap years using the Gregorian calendar rules: a year is a leap year if it's divisible by 4, except for century years, which must be divisible by 400. This means 2000 was a leap year, but 1900 was not.

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Day of Week Calculator

A day of the week calculator determines which weekday any date falls on—past, present, or future. It also provides the ISO week number, day-of-year count, and leap year status, making it useful for planning, research, and compliance.

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What is Day of Week Calculator?

A day of the week calculator is an online utility that determines the weekday name for any given date, along with additional context such as the ISO week number, day-of-year count, and leap year status.

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Start Using Day of Week Calculator Today

From satisfying curiosity about your birth day to verifying deadlines and planning events, the day of the week calculator gives you the answer instantly. It goes beyond the day name to show ISO week numbers, day-of-year counts, and leap year status—details that turn a simple lookup into genuinely useful information for planning and compliance.

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