📅 Date Calculator
Compute the difference between two dates, add or subtract days/weeks/months/years, count workdays excluding weekends and holidays, and calculate age. Auto-detects YYYY-MM-DD, YYYY/MM/DD, and Japanese date formats with timezone support.
✅ 100% free · no signup · browser-only
🔒 About Privacy
- ・All calculations happen in your browser
- ・Dates and holiday lists are never sent to any server
- ・No signup, no login, no payment
💡 Accepts YYYY-MM-DD, YYYY/MM/DD, and Japanese date formats
📖 How to Use
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1
Choose a modePick Difference, Add/Subtract, Workdays or Age from the top tabs.
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2
Enter datesUse YYYY-MM-DD, YYYY/MM/DD, or Japanese-style format.
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3
CalculateClick Calculate to see the result below.
❓ FAQ
Are my dates sent to your server?
No. All calculations run entirely in your browser via the JavaScript Date API. Your dates and holiday lists never leave your device.
How are leap years and month-ends handled?
Leap years follow the standard rule (div by 4, not 100, or div by 400). When adding months, dates beyond month-end are clamped (e.g. Jan 31 + 1 month = Feb 28).
How do I enter the holiday list?
One date per line, ideally in YYYY-MM-DD format. Blank lines are ignored. Weekends are excluded automatically.
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🐛 Found a bug or issue with this tool?
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