Accurate Date Duration Calculator with Leap Year Support

Accurate Date Duration Calculator with Leap Year Support

What it does

• Calculates the exact time between two dates in days, weeks, months, years, and business days.
• Correctly accounts for leap years (including Feb 29), varying month lengths, and time zones when times are included.
• Optionally includes/excludes start and end dates per user preference.

Key features

• Leap-year-aware: treats Feb 29 correctly when spanning leap years.
• Multiple output units: total days, weeks + days, months + days, years + months + days.
• Business days: excludes weekends and customizable holidays.
• Time component support: handles date-times with time zones and daylight saving shifts.
• Custom rules: choose whether to count the start/end date, specify working days, or use ⁄₃₆₀ conventions for financial calculations.
• Error handling: validates input formats and returns clear messages for invalid dates.

Example outputs

• Between 2020-02-27 and 2020-03-01 → 3 days (includes Feb 29).
• Between 2019-03-01 and 2020-03-01 → 1 year.
• Between 2024-02-28 and 2024-03-01 with start included → 3 days (2024 is leap year).

Implementation notes (brief)

• Use ISO 8601 for input.
• For days: compute absolute difference in days using proper calendar arithmetic.
• For years/months/days: subtract components with borrow logic, accounting for month lengths and leap-day presence.
• For business days: iterate or use formula excluding weekends and subtract holiday set.