Date Calculator
The Date Calculator performs period calculation between two dates, date addition/subtraction, business days calculation (excluding weekends and holidays), all in one tool. All processing is done in your browser, and no data is sent to servers.
What You Can Do
The Date Calculator is a comprehensive tool for period calculation, date addition/subtraction, business days calculation instantly. Perfect for payment deadline verification, project timeline management, and business day delivery calculations. All processing is done in your browser, and no data is sent to servers.
- ✅ Accurate Period Calculation: Automatically detects leap years and displays in years, months, days
- ✅ Business Days Calculation: Calculate business days excluding weekends and holidays
- ✅ Japanese Calendar Support: Input and display in Reiwa, Heisei, Showa
Easily calculate periods between dates, date addition/subtraction, and business days. Supports leap years for accurate results.
📅 Calculate Period Between Dates
📊 Result
Enter dates and click "Calculate Period"
📅 Add Days to Date
📊 Result
Enter date and number of days
📅 Subtract Days from Date
📊 Result
Enter date and number of days
📅 Calculate Business Days
* Excludes weekends and Japanese national holidays
📊 Result
Enter date and number of business days
💼 Use Cases
- Payment deadline verification - Calculate days from invoice or contract dates
- Business day delivery calculation - Find exact date for "10 business days later"
- Years of service calculation - Determine exact period from hire date
- Bank transfer prediction - Confirm deposit dates based on business days
- Japanese calendar document preparation - Easy conversion to Reiwa/Heisei
How to Use
📌 Basic Usage
Select a calculation mode from the tabs above, enter dates or days, and click the calculate button.
🔢 Calculation Modes
- Period: Calculate duration between two dates (e.g., How many days from date A to date B?)
- Add Days: Calculate date N days after a specific date (e.g., What date is 100 days from today?)
- Subtract Days: Calculate date N days before a specific date (e.g., What date was 30 days ago?)
- Business Days: Calculate excluding weekends and holidays (e.g., What date is 10 business days later?)
💡 Tips & Notes
Useful for project planning, deadline management, and anniversary tracking. Correctly handles leap years and supports both past and future dates. Japanese calendar input/display is also available.
❓ FAQ
📚 Practical Knowledge
Practical Applications
Date calculation is essential in many business and daily life scenarios. Particularly for contract period management, project deadline calculations, and payroll day counting where accuracy is critical. This tool is designed to provide instant accurate results for these practical situations.
About Business Days Calculation
Business days exclude Saturdays, Sundays, and holidays. Important for delivery deadline calculations and bank transfer predictions. This tool supports Japanese national holidays under the Public Holiday Law, including substitute holidays.
About Japanese Calendar
Japanese calendar (Wareki) is Japan's unique calendar system based on imperial era names. This tool supports eras from Meiji onwards.
- Reiwa: May 1, 2019 - present
- Heisei: January 8, 1989 - April 30, 2019
- Showa: December 25, 1926 - January 7, 1989
- Taisho: July 30, 1912 - December 24, 1926
- Meiji: January 25, 1868 - July 29, 1912
About ISO 8601 Standard
ISO 8601 is an international standard that defines date and time notation. This tool complies with the YYYY-MM-DD format (e.g., 2025-12-09), ensuring compatibility with systems worldwide.
- Format: YYYY-MM-DD (e.g., December 9, 2025 is "2025-12-09")
- Benefits: Language and region-independent, internationally consistent date notation
- Business Use: Standard for international trade, electronic contracts, database management, and global operations
Leap Year Calculation Rules
One of the most important elements in date calculation is leap year determination. Since Earth takes approximately 365.2422 days to orbit the Sun, we need to add an extra day every 4 years to compensate for the 6-hour difference.
- Divisible by 4: Leap year (2020, 2024, etc.)
- Divisible by 100: Common year (1900, 2100, etc.)
- Divisible by 400: Leap year (2000, 2400, etc.)
Example: 2000 is a leap year - Divisible by 400, so February has 29 days.
Example: 1900 is a common year - Divisible by 100 but not by 400, so February has 28 days.
Would you like to share your feedback? (Optional)