デイカウンター

Count days between dates, days since or until a date, and countdowns to events. Handles leap years with step-by-step solutions.

Your Input

Format: YYYY-MM-DD

Must be on or after start date

Select a calculation type, enter your dates, and click Count Days to see results with step-by-step solutions and visualizations.

完全なユーザーガイド

デイカウンターとは何ですか?

A day counter calculates the number of days between two dates, days since a past date, days until a future date, or a countdown to an event. It accounts for leap years, varying month lengths, and year boundaries.

Total days = End Date − Start Date  |  Business days = weekdays only (Mon–Fri)

Use it for project timelines, countdowns, age or tenure in days, and event planning.

Date Format

Use YYYY-MM-DD (e.g. 2025-02-15). Dates from year 1 to 9999 are supported.

計算の種類

間の日数

Exact number of days between two dates, plus weeks, months, hours, and business days (weekdays only).

あれからの日数

How many days have passed since a past date (e.g. since birth, since an event).

までの日数

How many days remain until a future date (deadlines, countdowns).

カウントダウン

Countdown to an event with optional name; shows days, weeks, months, hours, and minutes until the date.

この計算機の使い方

  1. Select a calculation type (Days Between, Days Since, Days Until, or Countdown)
  2. Enter the required dates (and optional event name for Countdown)
  3. Click 'Count Days' to see the result
  4. Review the main result, detail cards (when available), and step-by-step solution
  5. Use the chart for a visual breakdown where available
  6. Click 'Reset' to set all dates to today and clear results

結果を理解する

Main result

The total number of days, with a short formatted summary (e.g. X days, or X weeks Y days).

Detail cards

For Days Between and Countdown: breakdown into weeks, months, business days, and hours where applicable.

Step-by-step

Shows how the day count was calculated, including formulas and intermediate steps.

営業日について

Business days are weekdays (Monday–Friday); weekends are excluded. Used for project deadlines, shipping, work schedules, and contracts. Holidays are not excluded.

日の数え方

Simple subtraction: Total days = end date − start date.

相対デルタ: Precise years, months, and days; accounts for month lengths and leap years.

Business days: Count of weekdays (Mon–Fri) between the two dates.

重要な注意事項

  • All calculations account for leap years and varying month lengths.
  • Business days (Days Between) exclude weekends only; holidays are not excluded.
  • Use YYYY-MM-DD format. Dates must be between year 1 and 9999.

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