Does it know public holidays?

No. Japanese public holidays move with legislation, substitute days and the Happy Monday system, and single-year exceptions occur, as in the Tokyo Olympics year. A baked-in list would quietly become wrong. When holidays matter, take the current year's list published by the Cabinet Office.

How far back and forward does it go?

Broadly across the Gregorian calendar. Note that Japan moved to the solar calendar in 1873, so dates before that do not correspond to the lunisolar dates actually in use at the time. When researching a historical date, establish which calendar the source is written in first.

Can I pass the result to someone?

"Copy result" takes the weekday, date, day of the year and week number together, formatted to paste straight into an email or a chat.

Is the date I enter stored?

No, and nothing is sent. The calculation happens entirely in the page.

ISO week numbers are not calendar week numbers

An ISO 8601 week starts on Monday, and week 1 is the one containing the year's first Thursday. Under that rule, when 1 January falls on a Friday, Saturday or Sunday it belongs to week 52 or 53 of the previous year; and 29 December onwards can already be week 1 of the next year. The common "Sunday start, week 1 contains 1 January" scheme differs by up to a week, so confirm which definition a system expects before entering anything.

The leap-year rule completes a cycle every 400 years

Years divisible by 4 are leap years, except those divisible by 100, except again those divisible by 400. 1900 was not a leap year; 2000 was. Spreadsheets and programs that dropped the exception surfaced in numbers around 2000 precisely because the condition is only tested once a century. The next time it bites is 2100, which will not be a leap year.

"N business days" is not "N days"

The counts here are calendar days. Business-day arithmetic, skipping Saturdays and Sundays, lives on the date calculator page. Whether a contract's "within 7 days" means calendar or business days moves the deadline by about two days. Absent the words "business days", calendar days is the usual reading, though conventions differ by field.

Weekdays repeat on a 28-year cycle

In the Gregorian calendar, away from the century exceptions, the weekdays of a given date repeat every 28 years — which is why a 1998 calendar can be reused unchanged in 2026. The cycle breaks across 2100.

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What Day of the Week Was It?

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Enter any past or future date to get its weekday, how many days from today it is, the day of the year, the ISO week number, the number of days in that month and whether it is a leap year. You can also count N days from today.

Input

Look up by

Date

Output

Enter a date and the weekday and distance from today appear here.

ISO week numbers start on Monday, and week 1 is the one containing the first Thursday of the year. That is why a date in early January can fall in week 52 of the previous year.

Or type what you want to work out

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Why this one

It works in both directions: It answers both "what weekday is this date" and "what weekday is N days from today". The second is what deadline and delivery-date arithmetic actually needs, and a negative number reaches backwards. No counting across printed calendar pages.
More than the weekday: Day of the year, ISO week number, days in that month and whether it is a leap year, all at once. Business systems and project tools often refer to dates by week number, so being told "week 36" need not stop you.
The gap from today is shown too: How many days ahead of or behind today the date falls appears alongside. Days elapsed since something, or days remaining until something, without reaching for a second tool.

How to use

Choose the direction
Either "from a date" or "N days from today".
Enter a date or a number of days
Negative numbers work: -30 means thirty days ago. Leave the starting date blank to use today.
Read the result
Weekday and date, the gap from today, day of the year, ISO week, days in the month and leap-year status.

Good to know

ISO week numbers are not calendar week numbers: An ISO 8601 week starts on Monday, and week 1 is the one containing the year's first Thursday. Under that rule, when 1 January falls on a Friday, Saturday or Sunday it belongs to week 52 or 53 of the previous year; and 29 December onwards can already be week 1 of the next year. The common "Sunday start, week 1 contains 1 January" scheme differs by up to a week, so confirm which definition a system expects before entering anything.
The leap-year rule completes a cycle every 400 years: Years divisible by 4 are leap years, except those divisible by 100, except again those divisible by 400. 1900 was not a leap year; 2000 was. Spreadsheets and programs that dropped the exception surfaced in numbers around 2000 precisely because the condition is only tested once a century. The next time it bites is 2100, which will not be a leap year.
"N business days" is not "N days": The counts here are calendar days. Business-day arithmetic, skipping Saturdays and Sundays, lives on the date calculator page. Whether a contract's "within 7 days" means calendar or business days moves the deadline by about two days. Absent the words "business days", calendar days is the usual reading, though conventions differ by field.
Weekdays repeat on a 28-year cycle: In the Gregorian calendar, away from the century exceptions, the weekdays of a given date repeat every 28 years — which is why a 1998 calendar can be reused unchanged in 2026. The cycle breaks across 2100.

FAQ

Does it know public holidays?: No. Japanese public holidays move with legislation, substitute days and the Happy Monday system, and single-year exceptions occur, as in the Tokyo Olympics year. A baked-in list would quietly become wrong. When holidays matter, take the current year's list published by the Cabinet Office.
How far back and forward does it go?: Broadly across the Gregorian calendar. Note that Japan moved to the solar calendar in 1873, so dates before that do not correspond to the lunisolar dates actually in use at the time. When researching a historical date, establish which calendar the source is written in first.
Can I pass the result to someone?: "Copy result" takes the weekday, date, day of the year and week number together, formatted to paste straight into an email or a chat.
Is the date I enter stored?: No, and nothing is sent. The calculation happens entirely in the page.

Input

Output

Related tools

Why this one

How to use

Choose the direction

Enter a date or a number of days

Read the result

Good to know

FAQ