Date Calculator

Add/subtract time periods, calculate durations, and compute ages with flexible date formatting

Overview

The Date Calculator performs date arithmetic, calculates durations between dates, and determines exact ages. Whether you need to find a date 90 days from now, calculate someone’s age, or determine project duration, this tool handles all date calculations with precision including automatic leap year adjustments.

Tips

  1. Use ISO date format (YYYY-MM-DD) - This format is unambiguous, sorts correctly, and is the international standard. Avoid confusion between US (MM/DD/YYYY) and European (DD/MM/YYYY) formats.

  2. Be aware of month-end behavior - When adding months to dates like January 31, the result may be adjusted to the last day of the target month (e.g., Jan 31 + 1 month = Feb 28 or 29).

  3. Specify inclusive or exclusive - Be clear whether you’re counting boundary dates. “From Jan 1 to Jan 3” could be 2 days (exclusive end) or 3 days (inclusive).

  4. Remember leap year rules - Years divisible by 4 are leap years, except those divisible by 100 (unless also divisible by 400). So 2024 is a leap year, but 2100 is not.

  5. For business calculations, use the Working Days Calculator - This Date Calculator counts all calendar days. If you need to exclude weekends and holidays, use the dedicated Working Days Calculator tool instead.