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Day of Week Calculator Tool

Instantly calculate the day of the week for any date. Also shows Japanese era, holiday info, Chinese zodiac, zodiac sign, monthly calendar, and yearly same-weekday list.

Last updated: 2026/10/16 Calculator Feedback & bug reports
Holiday
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Japanese Era
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Chinese Zodiac
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Zodiac Sign
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Days from Today
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Rokuyo / Lunar date
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Calculation History
No history

How to Use

1

Enter a Date

Enter the year, month, and day. The day options auto-adjust based on month and year. Use preset buttons for quick input (Today, Next Holiday, Valentine's Day, etc.).

2

View the Day and Related Info

The day of the week is instantly displayed in large text. Japanese era, holiday status, Chinese zodiac, zodiac sign, and days difference are also shown.

3

Explore Calendar and Same-Weekday List

View the monthly calendar with holidays highlighted. Expand the yearly same-weekday list to see all dates sharing the same weekday.

4

Copy Results

Click "Copy Result" to copy date, weekday, Japanese era, zodiac, and more as formatted text to your clipboard.

About Day of Week Calculator

A web tool that instantly finds the day of the week for any date from year 1 to 9999. Shows Japanese era, holiday status, Chinese zodiac, zodiac sign, monthly calendar with holidays, and yearly same-weekday list. All processing happens in your browser with no data sent to any server.

Features

  • Instant Day CalculationThe day of the week appears instantly as you type. No button press needed.
  • Rich Additional InfoJapanese era, holiday check, Chinese zodiac, zodiac sign, and days difference - all in one view.
  • Monthly CalendarAuto-generated mini calendar with holidays color-coded. Navigate between months with arrow buttons.
  • Yearly Same-Weekday ListLists all dates in the year that fall on the same weekday, organized by month. Useful for scheduling.

Use Cases

  • Find what day of the week your birthday was
  • Check weekdays for upcoming events and holidays
  • Research what day historical events occurred on
  • Check Rokuyo (lucky days such as Taian) for weddings or moving
  • Schedule recurring weekly events

FAQ

Can I calculate dates from hundreds of years ago?
Yes, the tool supports dates from year 1 to 9999. Note that dates before 1582 (pre-Gregorian calendar) use proleptic Gregorian calendar calculations.
Which Japanese eras are supported?
Meiji (1868-) and later eras are supported: Reiwa, Heisei, Showa, Taisho, and Meiji with accurate boundary date detection.
How are Japanese holidays determined?
Japanese holidays are covered from July 20, 1948 (when the National Holiday Act took effect) through 2100, including every amendment: the moves of the Emperor's Birthday and Greenery Day, the Happy Monday system, the new Mountain Day, the 2019 enthronement holidays, and the 2020–2021 Olympic shifts. Substitute and citizens' holidays are included, and the results match the Cabinet Office list for 1955–2027 exactly. From 2028 onward they follow the current law, and equinox days are astronomical estimates (officially announced each February for the following year).
How is the Chinese zodiac determined?
The Chinese zodiac cycles through 12 animals based on the year: Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Sheep, Monkey, Rooster, Dog, and Boar.
How are holidays shown in the calendar?
Holidays appear in red text in the monthly calendar. Hover (or tap on mobile) to see the holiday name in a tooltip.
How does the yearly same-weekday list work?
It lists every date in the year that falls on the same weekday as your selected date, organized by month. Useful for planning recurring weekly events.
How are leap years handled?
Following Gregorian calendar rules: divisible by 4 = leap year, except divisible by 100 = common year, except divisible by 400 = leap year. February dates auto-adjust.
Can I copy the results?
Yes, click "Copy Result" to copy the date, weekday, Japanese era, zodiac info, and more as formatted text. The same-weekday list can also be copied separately.
Does it work on mobile?
Yes, the tool is fully responsive. The calendar supports tap to select dates, and all features work on smartphones and tablets.
How are Rokuyo and the lunar date calculated?
Rokuyo is determined by the month and day of the traditional Japanese lunisolar calendar (Taian, Shakko, Sensho, Tomobiki, Senbu, Butsumetsu). This tool uses a 1900–2100 calendar table built from NASA JPL ephemerides: new moons and principal solar terms in Japan time, the same principles used by the National Astronomical Observatory of Japan (2033 uses the commonly adopted leap 11th month). Rokuyo is a traditional custom with no scientific basis.

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