Duration Calculator

Add or subtract a duration from a base date-time locally in your browser with ISO Duration, local time, and Unix outputs.

Duration Calculator

A browser-based duration add/subtract calculator that applies a duration to a base date-time locally and returns ISO, Unix, and local-time outputs.

How to use

  1. Enter a base date-time and choose the matching time zone.
  2. Provide an ISO Duration or fill the split fields for days, hours, minutes, seconds, and milliseconds.
  3. Review both added and subtracted local date-time, ISO, Unix seconds, and Unix milliseconds in the result area.

Features

  • 100% local processing with no time data upload
  • Supports both ISO Duration and structured duration input
  • Returns both addition and subtraction results for planning and debugging

Why use this?

  • Useful for due-date projection, delay calculations, scheduling shifts, and time-window math
  • Useful for developers working with TTLs, expirations, scheduling windows, and offset validation
  • Free, fast, secure, and independent from third-party APIs

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