Date and time calculators, all in your browser
Compute the difference between two dates, add or subtract days, count business days, check week numbers, convert time zones, or run timers, countdowns and a pomodoro clock: every calculator here runs locally in your browser.
The calculations handle the calendar's real quirks: leap years, months of different lengths, daylight saving time switches and ISO week numbering. And because dates of birth or project deadlines are nobody's business, nothing you type is ever sent to a server.
All 28 tools in this category
- Date differenceCount the days, weeks, months and years between two dates, entirely in your browser, nothing uploaded.
- Add or subtract datesAdd or subtract years, months, weeks and days from any date, privately in your browser.
- Age calculatorWork out an exact age in years, months and days from a birth date, 100% in your browser.
- Day of the weekFind what day of the week any date falls on, plus day-of-year and week number. Private, offline.
- ISO week numberGet the ISO-8601 week number for any date, with the ISO week-year. Private and offline.
- Leap year checkerCheck whether any year is a leap year and why, with the nearest leap years. Offline, private.
- Days until a dateCount down the days until any date (or how many days ago it was). Private, in-browser.
- Quarter of a dateFind which calendar quarter a date belongs to, with the quarter's start and end. Offline.
- Time since a dateCount up the time elapsed since a past date, years, months, days and totals. In-browser.
- Business days calculatorCount working days (Mon–Fri) between two dates, excluding holidays. Private, in-browser.
- Time duration calculatorWork out the duration between two times of day, including overnight spans. In-browser.
- Nth weekday finderFind the date of the Nth weekday of a month (e.g. the 3rd Monday). Private, offline.
- Sleep cycle calculatorFind the best bedtimes or wake-up times based on 90-minute sleep cycles. In-browser.
- ISO 8601 duration converterParse and convert ISO 8601 durations (P1Y2M…) into components and seconds. In-browser.
- Date format converterConvert a date into ISO, US, European, dotted, compact and Unix formats. In-browser.
- Cron expression parserParse a cron expression and preview its next run times. Private, in-browser.
- ICS calendar generatorCreate a downloadable .ics calendar file for one or more events. No upload.
- Date detailsEverything about a date: weekday, week, quarter, leap year, zodiac and more. In-browser.
- Countdown timerCount down to any date and time, with a shareable link. Live, private, in-browser.
- Online timerA simple countdown timer with a sound alert. No signup, runs in your browser.
- Online stopwatchA precise stopwatch with laps. No signup, runs entirely in your browser.
- Pomodoro timerFocus with the Pomodoro technique: work/break intervals with sound. In-browser.
- Timezone converterConvert a date and time between any two IANA timezones. No upload, runs entirely in your browser.
- Timezone differenceSee the current UTC offset difference between any two IANA timezones. Private, in-browser.
- Timesheet calculatorCalculate daily worked hours, totals, overtime and pay from clock-in/out times. Private, offline, no upload.
- Sunrise & sunset timesGet accurate sunrise, sunset, solar noon and day length for any location and date. Private, offline, no upload.
- World clockLive local times for cities around the world, side by side. Private, offline, no upload.
- Moon phaseSee the moon phase for any date, its illumination and the next full and new moons. Private, offline, no upload.
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Frequently asked questions
Do these calculators account for leap years and DST?
Yes. They use your browser's calendar and time zone database, so leap years, daylight saving changes and ISO week rules are handled correctly, including for dates far in the past or future.
Is anything I type sent to a server?
No. Every calculation runs in your browser; dates of birth, deadlines and schedules stay on your device. The pages even work offline once loaded.
Can I save a result, like a countdown, to my calendar?
Several tools export an .ics calendar file, which is generated locally in your browser and opens in Google Calendar, Outlook or Apple Calendar.