📅 Date Arithmetic Tool

Add / Subtract Days Calculator

Add or subtract days, weeks, months, or years from any date. Calculate future and past dates instantly. Perfect for project deadlines, invoice due dates, and date planning.

⚙️ Calculation Settings

📆 Start Date

🔢 Amount to Add/Subtract

📏 Unit

📊 Result

Adding 30 days to:

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Day of Year

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Week Number

—

Days Remaining in Year

—

Leap Year

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⚡ Quick Presets

🎯 Popular Examples

📅 How to Add or Subtract Days from a Date

Our Add/Subtract Days Calculator makes date arithmetic simple and accurate. Whether you need to calculate a future date after adding 90 days, find a past date by subtracting weeks, or determine business day deadlines, this tool handles it all with precision.

Simply select your start date, choose the amount and unit (days, weeks, months, years, or business days), and click calculate. The tool automatically handles leap years, month lengths, and weekend exclusions for business day calculations.

📌 Pro Tip: Use Business Days for project deadlines, invoice due dates, and delivery estimates to exclude weekends from calculations.

🎯 Common Use Cases

📄 Invoice due dates (Net 15, 30, 60, 90 days)
⏰ Project deadline planning and milestones
🛡️ Warranty and expiration date calculation
📱 Subscription renewal reminders
🎂 Birthday and anniversary countdowns
🏖️ Vacation planning and return dates
💊 Medication schedule planning
📊 Financial investment maturity dates

✨ Features Overview

✓ Add or subtract days, weeks, months, years
✓ Business days calculation (excludes weekends)
✓ Automatic leap year handling
✓ Week number and day of year display
✓ Quick preset buttons for common values
✓ Popular example scenarios
✓ Real-time date formatting
✓ Dark/Light theme support

⚠️ Date Calculation Best Practices

Month calculations: Adding months handles varying month lengths correctly (Jan 31 + 1 month = Feb 28/29).
Business days: Only excludes Saturdays and Sundays. Does not account for public holidays.
Leap years: Our calculator correctly identifies leap years (divisible by 4, but not by 100 unless also by 400).
Year calculations: Adding years preserves the same month and day, handling February 29 correctly.
Negative values: Use the "Subtract" mode or negative numbers to calculate past dates.

❓ Frequently Asked Questions

1. What's the difference between days and business days?

Days include all calendar days (weekends and holidays). Business days exclude Saturdays and Sundays.

2. How are months handled?

Adding months preserves the same day number, adjusting for month lengths. Jan 31 + 1 month = Feb 28 (or 29 in leap years).

3. Does this handle leap years correctly?

Yes! February 29 is handled correctly, and adding years from Feb 29 works properly.

4. What's the maximum amount I can add/subtract?

Up to 9,999 units (days, weeks, months, or years). This covers approximately 27 years.

5. Is my data sent to a server?

No! All calculations happen locally in your browser. Your dates never leave your device.

6. Is this tool really free?

100% free forever! No sign-up, no watermarks, no hidden limits.

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