Date Calculator
Calculate the difference between dates or add/subtract days
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Date Difference
Review calendar spans in years, months, days, and raw day totals in one place.
Business Days
Business-day counts exclude weekends for lightweight planning and scheduling checks.
Add / Subtract Days
Project deadlines by adding or subtracting whole days from any base date.
Result Date
Enter dates to compare spans or project a new date.
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How to Use
Enter Your Values
Fill in the input fields with your numbers or parameters.
Get Instant Results
Results update automatically as you type — no submit button needed.
Copy or Save
Copy results to clipboard or use them in your workflow.
Why Use This Tool
100% Free
No hidden costs, no premium tiers — every feature is free.
No Installation
Runs entirely in your browser. No software to download or install.
Private & Secure
Your data never leaves your device. Nothing is uploaded to any server.
Works on Mobile
Fully responsive — use on your phone, tablet, or desktop.
Date Arithmetic: Adding, Subtracting, and Comparing Dates
Key Takeaways
- Date arithmetic must handle varying month lengths (28–31 days) and leap year rules correctly.
- Business day calculations exclude weekends and optionally public holidays, essential for project planning.
- The ISO 8601 standard defines unambiguous date formats (YYYY-MM-DD) to avoid regional confusion.
Date calculators solve a common yet surprisingly tricky problem: how many days are between two dates, or what date falls 90 business days from today? Unlike simple number arithmetic, date math must respect the irregularities of the Gregorian calendar — months of different lengths, leap years every four years (with century exceptions), and timezone boundaries.
97 leap years
Per 400-year Gregorian cycle
Common Use Cases
Project Deadlines
Calculate exact delivery dates by adding business days to a start date, excluding weekends and holidays.
Contract & Legal Dates
Determine notice periods, statute of limitations, or warranty expiration dates with precision.
Event Countdown
Find the exact number of days until a wedding, vacation, or product launch.
Age & Duration Math
Calculate the number of days between two events, such as employment duration or loan terms.
Practical Tips
Use ISO 8601 (YYYY-MM-DD) format to avoid ambiguity between DD/MM and MM/DD conventions.
When adding months, handle end-of-month overflow — adding 1 month to Jan 31 should yield Feb 28 (or 29).
For business-day calculations, always specify which public holidays to exclude — they vary by region.
Remember that time zones can shift the calendar date — 11 PM in New York is already the next day in London.
This tool is for informational and educational purposes. Verify results before using in critical applications.