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Date Calculator Tool

Calculate date ranges & elapsed days, weeks, dates X days after/before, and business days in real-time. Includes Japanese national holidays for accurate business day calculations.

Last updated: 2026/10/16 Calculator Feedback & bug reports
Days
- Days
- Weeks + Days
- Months + Days
- Years + Months + Days
days
Result Date
- Result Date

For one-tap 7, 30, 100 or 1000 days and a chart of dates before and after, try the Days From Date Calculator.

Weeks + Days
0 weeks 0 days
- Total Days
- Total Hours
- Full Weeks
- Years/Months/Days
Result Date
-

For today's week number, the weeks left this year and the weeks since January 1, try the Weeks Calculator.

Common Weeks Reference
Weeks Days Approx.
1weeks7days
4weeks28days~1 month
12weeks84days~3 months
13weeks91days~1 quarter
26weeks182days~6 months
40weeks280daysDue date (from LMP)
52weeks364days~1 year
Business Days
- Business Days
- Holidays
- Total Days
Excluded Holidays List

How to Use

1

Select Calculation Mode

Choose a tab: "Duration" for days/elapsed days between dates, "Add/Subtract" to find a date X days after/before, "Weeks" for week counts and weeks-to-date, or "Business Days" to count workdays excluding weekends and holidays.

2

Enter Dates

Enter start and end dates using the date inputs. Click "Today" for quick input. Set options like "Include start day" or "Business days only" as needed.

3

View & Copy Results

Results update in real-time as you type. View days, weeks, months, years, weekdays, and Japanese era at a glance. Use "Copy Result" to copy to clipboard.

About Date Calculator

A web tool for calculating date ranges, adding/subtracting days, and counting business days in real-time. Built-in Japanese national holiday data enables accurate business day calculations. All processing happens in your browser - no data is sent to any server.

Features

  • 4 Modes in OneDuration & elapsed days, weeks, date add/subtract, and business day counting - all in one tool with tab switching.
  • Auto Holiday ExclusionAutomatically excludes 16 Japanese national holidays + substitute holidays + citizens' holidays. Covers 1948–2100 including past law changes.
  • Real-time CalculationResults appear instantly as you enter dates. No button clicks needed.
  • Japanese Era SupportAutomatically displays Reiwa, Heisei, Showa, Taisho, and Meiji era years.

Use Cases

  • Project timeline and deadline calculations
  • Calculate resignation and job start dates
  • Anniversary countdowns
  • Invoice payment due dates (business day basis)
  • Contract period day counting

What This Date Calculator Can Do

Elapsed Days (Days Counter)

Use the "Duration" tab to instantly count the number of days between two dates. Track days since you started dating, days since joining a company, or days since a baby was born. Toggle whether to include the start day, and view days, weeks + days, years/months/days, and business days at a glance.

Weeks Calculation (How Many Weeks?)

Use the "Weeks" tab to calculate how many weeks and days are between two dates, or reverse-calculate a date from a number of weeks. Includes a pregnancy week reference and a quick reference table for 4, 12, and 52 weeks - handy for project timelines and training plans.

Open the Weeks Calculator →

Date After / Before Calculation

Use the "Add/Subtract" tab to find the date X days after or before a base date. Calculate 100 days later, 1000 days later, or 1 month later, and check whether the result is a holiday. Great for anniversaries, deadlines, and contract dates.

Open the Days From Date Calculator →

Business Days (Excluding Weekends & Holidays)

Use the "Business Days" tab to count workdays excluding weekends, holidays, and year-end/New Year periods. Automatically detects 16 Japanese national holidays plus substitute and citizens' holidays, with bank and government year-end presets - ideal for deadlines and payment due dates.

Related Date Calculation Tools

For the weeks between two dates and today's week number, use the Weeks Calculator; for the date N days from today, the Days From Date Calculator; and to convert between days, weeks, months and years, the Time Period Converter. Need only working days excluding weekends and holidays? The Business Day Calculator finds deadlines and payment due dates precisely. To check what day of the week a specific date falls on, count someone's age in days with the Age Calculator, or track the days remaining until an event with the Countdown Calculator. For more practical examples, see our date and day-counting guide.

FAQ

What can this tool do?
Three types of calculations: (1) Duration between two dates (days, weeks, months, years), (2) Add or subtract days from a date to find the result date, (3) Count business days excluding weekends and holidays. All calculated in real-time.
Which holidays are excluded in business day calculations?
All 16 Japanese national holidays (New Year's Day, Coming of Age Day, National Foundation Day, Emperor's Birthday, Vernal Equinox Day, Showa Day, Constitution Memorial Day, Greenery Day, Children's Day, Marine Day, Mountain Day, Respect for the Aged Day, Autumnal Equinox Day, Sports Day, Culture Day, Labor Thanksgiving Day) plus substitute holidays and citizens' holidays.
Can year-end/New Year holidays be excluded?
Yes, the Business Days tab offers year-end/New Year presets: "Bank (Dec 31 - Jan 3)" and "Government (Dec 29 - Jan 3)".
What does "Include start day" mean?
It determines whether to count the start date as day 1. For example, Jan 1 to Jan 3: excluding start = 2 days, including start = 3 days. Toggle based on your needs.
Are the Vernal/Autumnal Equinox dates accurate?
Yes. Equinox days use dates computed from the Sun's position with the NASA JPL ephemeris. They match the Cabinet Office list for 1955–2027; later years are astronomical estimates (officially announced each February for the following year).
How is the Japanese era displayed?
The corresponding era (Reiwa, Heisei, Showa, Taisho, Meiji) is automatically shown for result dates, with correct handling of era boundary dates.
Is my data saved?
No, all processing is done entirely in your browser. No data is sent to or stored on any server.
Can I use this on my smartphone?
Yes, the tool is fully responsive and works on smartphones, tablets, and desktops. Native date pickers are used on mobile devices.
Can I copy the results?
Yes, each tab has a "Copy Result" button that copies the calculation results to your clipboard in text format.
How far ahead does the holiday data cover?
Japanese national, substitute and citizens' holidays are covered from July 20, 1948 (when the National Holiday Act took effect) through 2100, including past law changes such as the Happy Monday system and the 2020–2021 Olympic shifts. Results match the Cabinet Office list for 1955–2027; from 2028 onward they follow the current law.
Can I calculate weeks (how many weeks)?
Yes, the "Weeks" tab calculates how many weeks and days are between two dates. The "Weeks to Date" mode also reverse-calculates a date X weeks after or before a base date. It includes a pregnancy week reference and a common-weeks quick reference table. For today's week number and the weeks left this year, try the dedicated Weeks Calculator.
Can I find a date X days after or before?
Yes, the "Add/Subtract" tab finds the date X days after or before a base date. Calculate 30, 100, or 1000 days later, and check the weekday, Japanese era, and whether the result is a holiday - useful for anniversaries and deadlines. The dedicated Days From Date Calculator adds one-tap day counts and a chart of dates.
Can I get the difference between two dates in years, months, and days?
Yes. The "Duration" tab shows the total number of days plus weeks + days, months + days, and years + months + days at once. It also displays the day of the week and Japanese era for both the start and end dates, making it easy to track contract or employment periods accurately. Use "Include start day" to toggle inclusive/exclusive counting.
What if I only want to count business days excluding weekends and holidays?
Use the "Business Days" tab to count days excluding weekends, national holidays, and year-end/New Year periods. For more detailed deadline calculations or to find a date a certain number of business days later, try the dedicated business day calculator as well.

Related Tools

Weeks Calculator Weeks and days between two dates, the date N weeks from today, and this week's number Days From Date Calculator The date N days after or before today or any date, with the day of the week Business Day Calculator Count business days and find the date N business days later Japanese Era / Western Year Converter Convert Japanese Era to Western year and vice versa with age, zodiac & more Age Calculator Calculate age, zodiac, milestone years, and more from your birthday

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Related Guides

Date & Day Calculations: Elapsed Days, Business Days, Days From Now A clear guide to counting days between two dates, business days (excluding holidays), a date N days before or after, and weeks. Learn leap-year and endpoint cautions, plus uses for deadline management and anniversaries. How to Count Business Days: Weekends, Holidays, and N Days Later Learn what a business day is from the ground up: working days excluding weekends and holidays, how to correctly count N business days later or earlier, the difference from calendar days, how to handle holidays and year-end breaks, and practical counting for deadlines and payment dates. Wareki to Seireki: Conversion Basics & Era Chart (Reiwa, Heisei, Showa) How to convert between Japanese era years and the Western calendar, with mental-math tips and a Reiwa/Heisei/Showa chart. Learn what Western year Reiwa starts from, era-change cautions, document use, and age calculation.