Date & Time Calculators
Add or Subtract Days Calculator
Calculate the resulting date after adding or subtracting a number of days from a starting date, handling month and year boundaries automatically.
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.
Decimal Hours to HMS Calculator
Convert decimal hours (like 7.75 hours) into standard hours, minutes, and seconds format, useful for reading timesheets.
Event RSVP Tracker
Track event RSVPs by converting Yes, No, and Maybe counts into response rate, acceptance rate, and expected attendee headcount.
Julian Date Calculator
Convert a Gregorian calendar date into its Julian Day Number using the standard astronomical conversion algorithm.
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.
Moon Age Calculator
Calculate the moon's current age in days within its lunar cycle and its phase for any given calendar date.
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 Format Converter Calculator
Convert a 24-hour (military) time into standard 12-hour AM/PM format.
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.
Unix Timestamp Converter Calculator
Convert a Unix timestamp (seconds since January 1, 1970) into a readable calendar date and time in UTC.
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.
Counting Days the Way People Actually Mean
"30 days" means something different depending on context — calendar days, business days, or days until a specific weekday all count differently, and mixing them up is a common source of missed deadlines. These twelve calculators handle date and time math across all of those interpretations.
Popular Date & Time Calculators
- Age Calculator — calculates exact age in years, months, and days from a birth date.
- Time Zone Calculator — converts a specific time between two time zones, accounting for daylight saving differences.
- Week Number Calculator — finds the ISO week number for any given date.
- Leap Year Calculator — checks whether a given year is a leap year using the standard divisibility rule.
Planning an event with a countdown? See the Countdown Calculator, or check broader scheduling tools in Productivity Calculators.