Date & Time Tools
Work out date differences, ages, business days, countdowns, leap years and timestamp conversions.
16 tools · all free, all run in your browser
Add Business Days to a Date
Find the date that falls a set number of working days after (or before) any start date, skipping weekends and any holidays you list.
Open toolAdd or Subtract Days
Add or subtract days, weeks, months or years from any date and see the resulting date in several formats.
Open toolAge Calculator
Calculate an exact age in years, months and days from a birth date, plus total days lived and the countdown to the next birthday.
Open toolBirth Year Calculator
Work out the year someone was born from their age on a given date, with both possible birth years and the exact range of birth dates.
Open toolBusiness Days Calculator
Count the working days between two dates, choosing whether Saturday and Sunday count as working days.
Open toolDate Difference Calculator
Work out exactly how much time sits between two dates, in years, months, days, weeks, hours and minutes.
Open toolDay of the Week Calculator
Find which day of the week any date fell on, past or future, along with the week number, day of the year and zodiac sign.
Open toolDays From Today
Find the date a number of days or weeks from today, or before today, with the weekday, ISO date and a chart of 7 to 365 days out.
Open toolDays Until Calculator
Count how many days, weeks, months and working days are left until a date, or how long ago it was, with a countdown to upcoming holidays.
Open toolHours Calculator
Work out the hours and minutes between a start time and an end time, minus an optional break, as h:mm and decimal hours.
Open toolKorean Age Calculator
Work out your Korean age (세는 나이), international age (만 나이) and year age (연 나이) from a date of birth.
Open toolLeap Year Checker
Check whether any year is a leap year and see exactly which part of the divisible-by-4/100/400 rule decided it.
Open toolTime Calculator
Add or subtract a list of durations in hours, minutes and seconds, with the carry done for you and a running total per line.
Open toolTime Zone Converter
Convert a date and time between two time zones, correctly accounting for daylight saving.
Open toolUnix Timestamp Converter
Convert a Unix timestamp to a human-readable date, or turn any date into seconds and milliseconds since the epoch.
Open toolWeek Number Calculator
Find the ISO-8601 week number for any date, along with the day of year, quarter and days left in the year.
Open toolDate arithmetic is deceptively hard. Months have different lengths, leap years follow a rule with two exceptions, weeks can straddle a year boundary, and timestamps are counted from an arbitrary moment in 1970. These tools handle the awkward cases properly so you can answer practical questions — how old someone is today, how many working days remain before a deadline, or what a Unix timestamp in a log file actually means in your local time.
The leap year rule in full
A year is a leap year if it is divisible by 4, except that century years are not, unless they are divisible by 400. So 1900 was not a leap year but 2000 was. The rule exists because the Earth's orbit takes roughly 365.2422 days; adding a day every four years slightly overcorrects, and the century exceptions claw that back. The Gregorian calendar is accurate to about one day in 3,000 years, which is why the rule is fiddly rather than simple.
Counting the difference between two dates
There are two reasonable answers to how far apart two dates are, and they disagree. A calendar-aware breakdown gives years, months and days by walking the calendar, which is what people mean by age. A total-days count simply divides the elapsed time, which is what billing and deadlines usually need. Both are shown here. Business-day counts add another wrinkle: they exclude weekends, and public holidays vary so much by country and region that they must be handled separately.
Unix timestamps and the 2038 problem
A Unix timestamp counts seconds since 1 January 1970 at 00:00 UTC, ignoring leap seconds. It is timezone-independent, which is exactly why it is the standard format for logs, databases and APIs — the same instant reads identically everywhere, and only display needs localising. Systems that store it as a signed 32-bit integer overflow on 19 January 2038, the so-called Year 2038 problem; modern platforms use 64-bit values, which pushes the limit far beyond any practical horizon. Timestamps also appear in milliseconds, notably in JavaScript, which is why a value roughly a thousand times too large usually just needs dividing.