OmniWhen

All the time-based calculators you'll ever need and more

Try the calculators ↓
📏

Durations & Intervals

Calculate differences between dates, shift times, and convert between HH:MM:SS and decimal formats.
🎂

Age & Life

Exact ages, days until birthday, time-since-then milestones, and pregnancy progress.
💼

Business & Productivity

Business days, timesheets, next-weekday lookups, Pomodoro planning, date-range breakdowns.
🎉

Holidays & Countdowns

Christmas, Halloween, New Year's Eve, Easter — plus a live countdown to any moment you choose.
🔧

Tools & Conversions

World clock, stopwatch, time zones, Unix timestamps, sleep cycles, Roman numerals & more.
🌍

Live World Clock

Watch the time in multiple cities update second by second — saved between visits.
⏱️

Stopwatch & Laps

High-precision stopwatch with hundredths and lap splits.
⏲️

Live Countdown

Pick any future moment and watch the timer tick down in real time.
Explore all 26 calculators ↓

All 26 Time Calculators

Free, fast, and works on every device. Click any calculator below to jump straight to it.

📏 Durations & Intervals

  • Duration Between Dates — exact time between two moments.
  • Add or Subtract Time — shift a date by days/hours/minutes/seconds.
  • Hours ↔ Decimal Converter — convert HH:MM:SS to decimal hours.

🎂 Age & Life

  • Age Calculator — exact age in years, months and days.
  • Days Until Birthday — countdown to your next birthday.
  • Time Since Date — how long ago something happened.
  • Pregnancy Due Date — estimated due date from your last period.

💼 Business & Productivity

  • Business Days Calculator — add or subtract working days.
  • Count Business Days — working days between two dates.
  • Next Weekday — find the next Monday, Friday, etc.
  • Workday Hours / Timesheet — clock-in to clock-out with lunch.
  • Pomodoro Planner — schedule focused work sessions.
  • Date Range Breakdown — presets like "this week" with breakdown.

🎉 Holidays & Countdowns

  • Time Until Christmas
  • Time Until Halloween
  • Time Until New Year's Eve
  • Easter Date Calculator — Easter Sunday for any year.
  • Live Countdown Timer — countdown to any moment.

🔧 Tools & Conversions

  • Leap Year Checker
  • Time Zone Converter — DST-aware IANA conversion.
  • Unix Timestamp Converter — date ↔ seconds/ms.
  • Day of Year — DOY and ISO week.
  • Sleep Cycle Planner — 90-minute cycle planner.
  • World Clock — live, multi-zone.
  • Stopwatch & Lap Timer
  • Roman Numerals — year ↔ MMXXVI.

Frequently asked questions

Is OmniWhen free to use?
Yes — every calculator on OmniWhen is free, with no sign-up, no ads, and no usage limits. Use them as much as you like on any device.
Does OmniWhen work on mobile and offline?
All 26 calculators are mobile-friendly and use no server-side processing — your inputs never leave your device. Add OmniWhen to your home screen for an installable, offline-capable web-app experience.
Where do my saved settings live (theme, background, pinned calculators)?
Locally in your browser via localStorage. Nothing is sent to any server. Clearing your site data resets the customizations.
Can I link directly to a specific calculator?
Yes — every calculator has its own clean URL like omniwhen.com/age-calculator.html, and the home page also supports hash deep links such as #calc-age that scroll to the right tool.
How accurate are the calculators?
Date math is exact to the millisecond. Time-zone conversions use the IANA database shipped with your browser, so DST transitions are handled correctly. Health-style tools like the pregnancy due-date estimator are population estimates only — always consult a professional.
Are there keyboard shortcuts?
Yes. Press ? or Ctrl+/ to open the shortcuts modal. Ctrl+K focuses search; number keys 1–5 jump between category tabs; P opens the Pinned tab when you have any pinned.
OmniWhen — time calculators & utilities
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