JP

Weeks Calculator Tool

Calculate how many weeks and days between two dates, or find a date by adding weeks. With Japanese era display, holiday detection, and preset shortcuts.

Last updated: 2026/03/01 Calculator
0 weeks 0 days
0 Total Days
0 Total Hours
0 Full Weeks
0 Remaining Days
weeks + days
Common Weeks Reference
Weeks Days Approx.
1weeks7days
2weeks14days
4weeks28days~1 month
8weeks56days~2 months
12weeks84days~3 months
13weeks91days~1 quarter
26weeks182days~6 months
40weeks280daysDue date (from LMP)
52weeks364days~1 year
104weeks728days~2 years

How to Use

1

Choose a Tab

Use "Period to Weeks" to calculate weeks between two dates, or "Weeks to Date" to find a date by adding/subtracting weeks. Preset buttons provide one-click shortcuts.

2

Enter Dates or Weeks

Enter dates in the input fields or click "Today" to set today's date. Results update in real-time as you type.

3

Review & Copy Results

Check the detailed results including weeks, days, year/month/day breakdown, Japanese era, and weekday. Click "Copy Result" to copy to clipboard.

About Weeks Calculator

A web tool that instantly calculates the number of weeks and days between two dates. Also supports reverse calculation from weeks to dates. Features Japanese era display, holiday detection, and pregnancy week reference. All processing happens in your browser with no data sent externally.

Features

  • Real-time CalculationResults update instantly as you enter dates. No need to click a calculate button.
  • Bidirectional CalculationCalculate weeks from a date range, or find a date from a number of weeks. Two modes for all your needs.
  • Japanese Era & HolidaysJapanese era display and holiday detection with 16 national holidays plus substitute holidays.
  • Preset ShortcutsFive presets: Since Jan 1, Since Apr 1, 4/12/52 weeks later for quick one-click calculations.

Use Cases

  • Check how many weeks since the start of the year
  • Calculate project duration in weeks
  • Track weeks until a due date
  • Find a date 12 weeks out for training plans
  • Check remaining weeks in a semester or quarter

FAQ

What does "Include start date" mean?
When enabled, the start date itself counts as day 1. For example, March 1 to March 7 would be 7 days (1 week 0 days) with it on, or 6 days (0 weeks 6 days) with it off.
Can I calculate a date from weeks?
Yes, use the "Weeks to Date" tab. Enter a base date, number of weeks, and optional extra days to find the resulting date forward or backward.
Can I use this for pregnancy week calculations?
You can use it as a reference. Set your last menstrual period as the start date to see the current week. For results within 40 weeks, trimester information is shown. Always consult your doctor for medical decisions.
What presets are available?
Five presets: "Since Jan 1" and "Since Apr 1" (Japan's fiscal year), plus "4 Weeks Later", "12 Weeks Later", and "52 Weeks Later".
How is the Japanese era displayed?
The corresponding era (Reiwa, Heisei, Showa, Taisho, Meiji) is automatically shown for each date in the results.
How does holiday detection work?
In the "Weeks to Date" tab, if the result date falls on a Japanese national holiday, the holiday name is displayed. Includes 16 holidays plus substitute holidays.
What if the start date is after the end date?
The tool handles this gracefully, showing the result as a positive value with a note that the start date is after the end date.
Can I copy the results?
Yes, click "Copy Result" to copy the calculation results to your clipboard in text format.
Does it work on mobile devices?
Yes, the tool is fully responsive and works on smartphones, tablets, and desktops.
Is my data saved?
No, all calculations happen in your browser. No data is sent to any server, and inputs are cleared when you close the page.

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