Time & Date Calculators
Durations, date differences, deadlines and time zones.
- Add Days Calculator Add or subtract any number of days from a date to find the resulting date and weekday, with the weekday-only equivalent and common offsets.
- Age Calculator Find exact age in years, months and days from a date of birth, with totals in months, weeks, days and hours and the next birthday.
- Birthday Calculator Count down to your next birthday, find the weekday it falls on and the day you were born, plus your star sign and birthstone.
- Business Days Calculator Count the business days between two dates, excluding weekends and any holidays you list, with the calendar breakdown and working hours.
- Countdown Calculator Count down to any date and time in days, hours and minutes, with totals in hours, minutes and seconds — for events, launches and New Year.
- Date Calculator Add or subtract years, months, weeks and days from any date to find the resulting date and weekday, with month-end dates handled.
- Date Difference Calculator Find the difference between two dates in years, months and days, plus totals in weeks, days, hours, minutes and weekdays.
- Day of the Week Calculator Find the day of the week for any date in history or the future, with the day of the year and the Zeller's congruence working.
- Days Between Dates Calculator Count the days between two dates, with or without the end date, split into weekdays and weekend days and into weeks and days.
- Days Until Calculator Count the days until any date — a holiday, birthday or event — with weeks, weekdays, weekends and sleeps, or the days since a past date.
- Deadline Calculator Find a deadline a number of calendar or business days after a start date, skipping weekends and holidays, with weekend roll-over.
- Decimal Time Converter Convert decimal hours to hours, minutes and seconds — or hours and minutes to decimal hours — for timesheets, payroll and invoicing.
- Half Birthday Calculator Find your half birthday — six months after your birthday — with a countdown, the age you turn and the exact midpoint between birthdays.
- Hours Calculator Find the hours and minutes between two times — including overnight and across dates — less any break, in hours, decimal and minutes.
- Lap Average Calculator Average a set of lap times with the total, fastest and slowest laps, pacing consistency, each lap against the average, and speed.
- Leap Year Calculator Check whether any year is a leap year with the rule explained, find the previous and next leap years, or count leap years in a range.
- Military Time Converter Convert standard 12-hour am/pm time to 24-hour military time and back, with how it is said aloud, like fourteen thirty hours.
- Minutes to Hours Calculator Convert minutes to hours and minutes and to decimal hours — or hours to minutes — with seconds and days, and the working shown.
- Months Between Dates Calculator Find the number of months between two dates — whole months and days, as a decimal, and by average month length — plus months touched.
- Moon Phase Calculator Find the Moon's phase, age and illumination for any date, with the exact times of the next new, first quarter, full and last quarter moons.
- Sunrise Sunset Calculator Find sunrise, sunset, solar noon, day length and civil twilight for any date and place, in the local time zone with daylight saving applied.
- Time Addition Calculator Add up a list of times and durations — like 1:45, 2h 30m or 50m — or subtract some, to get the total in h:mm:ss, words and decimal hours.
- Time Card Calculator Total a week of shifts from start and end times and breaks, split regular and overtime hours, and work out pay with an overtime rate.
- Time Division Calculator Divide a duration by a number to split it into equal parts, or by another duration to see how many times it fits, with remainders.
- Time Duration Calculator Find the exact duration between two times to the second — in hours, minutes and seconds, h:mm:ss, decimal hours and total seconds.
- Time Multiplication Calculator Multiply a duration in hours, minutes and seconds by any number, such as a 1:45:30 task repeated 6 times, with the total in h:mm:ss and decimal hours.
- Time Zone Converter Convert a date and time between world time zones — London, New York, Karachi, Dubai, India, Tokyo and more — with daylight saving applied.
- Timecode Calculator Add, subtract and convert SMPTE timecode at 23.976, 24, 25, 29.97 drop-frame, 30, 50, 59.94 or 60 fps, with frame counts and real running time.
- Timesheet Calculator Total timesheet entries by client, project or task, round them to a billing increment, and work out the amount at an hourly rate.
- Unix Timestamp Converter Convert a Unix timestamp (seconds or milliseconds since 1970) to a date and time in UTC and any time zone, or a date back to a timestamp.
- Week Number Calculator Find the ISO week number of any date, with the week's Monday-to-Sunday dates and the US week number — or the dates of any week.
- Working Hours Calculator Find hours worked per day, week and year from start and end times and unpaid breaks, including overnight shifts, with optional pay.
- Years Between Dates Calculator Find the number of years between two dates — whole years, decimal years and years, months and days — with the leap days crossed.
A Guide to Time & Date Calculators
Date arithmetic looks like the easiest kind of calculation and is quietly one of the hardest. Months have different lengths, years sometimes have an extra day, time zones shift twice a year in some places and never in others, and the answer to "how many days between these two dates" depends on whether you count both ends.
The thirty-three calculators here handle those edge cases explicitly rather than averaging over them. Each states the convention it is using, because on this topic the convention is most of the answer.
Days between dates
Six calculators, and the reason there are several is that "the difference between two dates" is not one question.
The Days Between Dates Calculator gives the plain count. The Date Difference Calculator expresses the same gap in years, months and days together, which is what you want for an anniversary or a tenancy rather than a four-digit number of days. Months Between Dates and Years Between Dates report in a single unit, which requires a decision about partial periods that the calculator makes visible rather than silently.
The Add Days Calculator and the general Date Calculator work in the other direction, from a date and an interval to a new date.
The inclusive-exclusive question is the one that catches people. Monday to Friday is four days apart and five working days, and both answers are correct for different purposes. Every calculator in this group says which it has given you.
Business days
Four calculators for working time rather than elapsed time. The Business Days Calculator counts only working days between two dates, excluding weekends and the holidays you specify, which is how contractual and legal deadlines are actually counted.
The Working Hours Calculator, Time Card Calculator and Timesheet calculator total worked time across a day, week or pay period, handling breaks and overnight shifts. The overnight case is where most timesheet arithmetic goes wrong, because a shift ending at 02:00 has an end time numerically smaller than its start.
Duration and time arithmetic
Nine calculators for adding, dividing and converting spans of time. The Time Duration Calculator gives the gap between two clock times, and the Hours Calculator totals a list of them.
Time Addition, Time Multiplication and Time Division calculators do arithmetic in base sixty, which is where mental arithmetic fails most reliably: 45 minutes times three is not 135 minutes on a clock face.
Two converters handle the two ways time is written. Minutes to Hours and the Decimal Time Converter move between the sexagesimal form on a clock and the decimal form payroll systems use. This is a real source of underpayment: 7 hours 30 minutes is 7.5 hours, not 7.3, and entering the latter costs twelve minutes a day.
The Lap Average Calculator averages lap times, and the Timecode Calculator works in frames for video editing, where the frame rate makes the arithmetic non-decimal in a second way.
Clock formats and time zones
The Military Time Converter handles the 24-hour and 12-hour forms in both directions, including the two cases that cause the most confusion: midnight and noon, where 12 AM and 12 PM are counterintuitive and 0000 and 1200 are not.
The Time Zone Converter converts between zones with their daylight saving rules, which do not change on the same dates in different countries and do not exist at all in many. The Unix Timestamp Converter moves between human dates and the seconds count that software stores.
Age
Three calculators. The Age Calculator gives an exact age in years, months and days, and handles the 29 February birthday case, which has no unambiguous answer in a non-leap year and so is stated rather than assumed.
The Birthday Calculator gives the day of the week you were born and the time until the next one, and the Half Birthday Calculator finds the midpoint, which is not simply six months later for every date.
Countdowns and deadlines
The Countdown Calculator and Days Until Calculator count forward to a date, and the Deadline Calculator works out a due date from a start and a duration, with the option to count in working days rather than calendar days.
These are the only calculators on this site whose answer changes while you read it, which is why they are not pre-rendered like the rest: a cached countdown is wrong by definition.
Calendar facts
Three calculators. The Day of Week Calculator gives the weekday for any date, past or future. The Leap Year Calculator applies the full rule rather than the divisible-by-four shortcut: a year divisible by 100 is not a leap year unless it is also divisible by 400, which is why 1900 was not and 2000 was.
The Week Number Calculator gives the ISO week number, which is used throughout business and industry in Europe and defined in a way that occasionally puts the first days of January in the last week of the previous year.
Sun and moon
The Sunrise Sunset Calculator computes times for any date and location, and the Moon Phase Calculator gives the phase and the dates of the next new and full moon. Both are astronomical rather than tabulated, so they work for any year rather than a fixed range.
Why date arithmetic is harder than it looks
It is worth understanding why this category needs thirty-three calculators when the underlying quantity is just a count of days.
Calendar units are not uniform. A month is between 28 and 31 days, so "three months from now" has no single definition: from 31 January it can reasonably be 30 April or 1 May, and software disagrees about which. A year is 365 or 366 days, so an age in years is exact while an age in days is not a fixed multiple of it.
Clock units are base sixty, which breaks the decimal intuition everybody has. Adding times, averaging them and dividing them all require carrying at 60 rather than at 10, and the error when you forget is small enough to go unnoticed and large enough to matter over a pay period.
Time zones are political rather than geographical. Offsets are not all whole hours, daylight saving start dates differ by country and change by legislation, and some places have abolished it. No formula derives this; it has to be looked up.
And the day boundary is a convention too. A shift, a flight or a deadline that crosses midnight needs a date as well as a time to be unambiguous, which is why the calculators that handle overnight cases ask for both.
The conventions worth knowing
Four decisions sit underneath most date arithmetic, and knowing which one a tool has made explains almost every surprising answer.
Whether both end dates are counted, which decides between four and five for Monday to Friday. Whether partial months count, which decides whether 15 January to 14 February is one month or zero. Whether weekends and holidays are excluded, which separates calendar from working days. And which day starts the week, which is Sunday in the United States and Monday under the ISO standard used almost everywhere else.
Every calculator above states its choice on the page. When two tools disagree about a date difference, this is nearly always why, and neither of them is broken.
If a date matters contractually, check the convention before the arithmetic. A deadline counted in working days from a Friday falls a week later than one counted in calendar days, and that is a difference nobody notices until it has already passed.