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Date, Time & Calendar Tools

Calculate dates, work hours, calendar weeks and time zones.

How to use this tool
  1. Choose the workflow and enter the requested details.
  2. Review options and run or save the selected action.
  3. Check the result and export or save where available.

Limits and requirements

Provider-based features require connectivity and configured services.

Check each operation’s notes. Some workflows run on your device; others use the OneTabTool server or a named third-party service. Don’t assume every tool processes files in the same way.

Available operations

  • Date difference / days until
  • Add / subtract days
  • Age / days lived
  • Business-day counter

    Excludes Saturday/Sunday and dates you supply. Includes both endpoints.

  • ISO week, quarter & leap year
  • Time duration
  • Work hours / time card

    If end is earlier than start, the shift crosses midnight.

  • Timezone converter / world clock
  • Date formatter
  • Gregorian ↔ Hijri converter

    Uses your browser’s Umm al-Qura calendar. Reverse conversion supports Gregorian years 1900–2100. Local moon-sighting dates may differ.

  • Pregnancy due-date estimate

    Calendar estimate only; clinical dating may differ.

  • Cycle / ovulation estimate

    Not suitable for contraception; cycles and ovulation vary.

  • Sleep-cycle planner

    Uses a simplified 90-minute cycle assumption; actual sleep cycles vary.

  • Sunrise, sunset & daylight hours

    Astronomical estimates in the selected timezone. Terrain and local horizon can change observed times.

  • Moon phase & illumination
  • Time since a milestone
  • Fasting duration from entered times

    Duration only. Enter the start/end times from your chosen local timetable.

  • Distance between cities

    City lookup uses Open-Meteo/GeoNames. Ambiguous searches require you to choose a returned ID. Straight-line distance, not a driving route.

  • Country information lookup

    Bundled country geography data from mledoze/countries (ODbL), snapshot 19 October 2026. No live population or visa information. Dataset and license: /data/countries/.

  • Public holiday calendar

    Nager.Date public holiday data. Coverage varies; regional holidays may only apply to listed subdivisions. Check local notices before relying on closures.

  • Ramadan calculated calendar

    AlAdhan calculated times. Check your local mosque/authority for the applicable method, high-latitude rules and moon-sighting dates. The calendar is not a religious determination.

  • Location-based dawn-to-sunset interval

    AlAdhan calculated times. Check your local mosque/authority for the applicable method, high-latitude rules and moon-sighting dates. The calendar is not a religious determination. Fajr and Imsak are shown separately; selecting an interval does not establish the religious start of fasting.

Questions about Date, Time & Calendar Tools

What does Date, Time & Calendar Tools do?

Calculate dates, work hours, calendar weeks and time zones.

How do I use Date, Time & Calendar Tools?

Choose the workflow and enter the requested details. Review options and run or save the selected action. Check the result and export or save where available.

What should I check before using the result?

Provider-based features require connectivity and configured services.

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