Date & Time Calculators
Age Calculator
Find exact age in years, months, and days from a birth date, plus total days lived and a countdown to the next birthday, as of any chosen date.
Business Days Calculator
Calculate business days between two dates by excluding Saturdays and Sundays, along with the total calendar and weekend day counts.
Calendar Calculator
Generate a full month calendar grid for any month and year, choosing whether the week starts on Sunday or Monday.
Countdown Calculator
Count down to any target date and time, showing days, hours, minutes, and seconds remaining, or elapsed time if the date has passed.
Date Difference Calculator
Calculate the difference between two dates as a calendar breakdown of years, months, and days, plus totals in months, weeks, and days.
Day Counter
Count the total days between two dates, with an option to include or exclude the end date, shown in both days and weeks.
Event RSVP Tracker
Track event RSVPs by converting Yes, No, and Maybe counts into response rate, acceptance rate, and expected attendee headcount.
Leap Year Calculator
Check whether a given year is a leap year under the Gregorian calendar rule, and find the nearest previous and next leap years.
Prayer Time Calculator
Calculate Fajr, Sunrise, Dhuhr, Asr, Maghrib, and Isha prayer times from date, latitude, longitude, and a chosen calculation method.
Time Conversion Calculator
Convert between seconds, minutes, hours, days, weeks, months, years, and decades using exact and average Gregorian calendar factors.
Time Duration Calculator
Calculate the exact duration between a start and end date and time, broken into days, hours, minutes, and seconds, with totals.
Time Zone Calculator
Convert a date and time between two UTC offsets by routing through UTC, showing the converted time and any calendar day change.
Week Number Calculator
Find the ISO 8601 week number and week-numbering year for any date, including edge cases where January dates belong to the prior year.
Weekday Calculator
Find the day of the week, weekend status, calendar quarter, ISO week number, and day of year for any date in one calculation.
Calendar Math Is Trickier Than Counting Days
Date and time math looks simple until leap years, time zones, and business-day exclusions enter the picture — the number of days between two dates depends on which months and years are crossed, and a countdown across time zones needs to account for daylight saving shifts that don't happen on the same date everywhere. Fourteen calculators here handle that complexity directly.
Popular Date & Time Calculators
Highlights across scheduling, counting, and conversion:
- Age Calculator — finds exact age in years, months, and days from a birth date.
- Date Difference Calculator — finds the exact span between two dates in days, weeks, or months.
- Business Days Calculator — counts working days between dates, excluding weekends and optionally holidays.
- Time Zone Calculator — converts a specific time across time zones, accounting for daylight saving differences.
- Leap Year Calculator — checks whether a given year is a leap year under the Gregorian calendar rule.
Why Leap Year Has an Exception to Its Exception
The familiar "divisible by 4" leap year rule has two nested exceptions: a year divisible by 100 is not a leap year, unless it's also divisible by 400 — which is why 2000 was a leap year but 1900 and 2100 are not. This adjustment exists because a true solar year is about 365.2422 days, not exactly 365.25, and the extra correction keeps the Gregorian calendar aligned with the seasons over centuries rather than drifting by roughly a day every 128 years, which is the error size of the simpler rule alone.
Frequently Asked Questions
Why do business days calculators need a country or region setting?
Public holidays differ significantly by country and even by region within a country, so an accurate working-day count needs to know which holiday calendar applies.
Does a time zone calculator account for daylight saving time automatically?
It should for regions currently observing it, but daylight saving start and end dates vary by country, and some regions don't observe it at all, which is why the specific date of a conversion matters, not just the time zone name.
Explore More
Managing project schedules instead of personal dates? See the Project Management Calculators, or check travel-specific time zone math in the Travel Calculators.