Date and time
Compare dates, shift a date, count workdays or inspect calendar facts with explicit rules.
Dates are processed in this browser and are not sent to a server.
Proleptic Gregorian calendar · ISO 8601 weeks: Monday first, week 1 contains January 4.
YYYY-MM-DD or YYYY-MM-DDTHH:mm[:ss], optionally with Z or ±HH:mm.
Years 0001–9999. Offsets: whole days or hours, up to ±1,000,000. Holidays: at most 1,000 lines and 20,000 characters.
Enter dates or load an example.
Use this date calculator when a project interval, an anniversary or a timestamp spans a boundary that a simple division by 24 would miss. A calendar date and an elapsed duration answer different questions.
Start with the clock and timezone when you need hours. Choose date-only modes for business days, ISO week information or age, where a wall-clock offset should not change the answer.
The date calculator shows one calendar day and 23 elapsed hours for noon on March 9 to noon on March 10, 2024 in New York. Add one day to keep the wall time; add 24 hours to advance by a fixed duration.
Set the weekdays your schedule excludes and list your own holiday dates. The report separates weekend exclusions from additional holidays, so a holiday falling on a weekend cannot silently subtract another day.
Business days, date information and age require YYYY-MM-DD. Difference and add modes also accept a time. Without an offset, that time belongs to the selected IANA zone; a supplied offset identifies the instant and the zone controls its display.
The default day count includes the start and excludes the end. Include the end date when counting both calendar dates. This switch never changes elapsed hours, and it is not available for age or time addition.
Automatic calculation waits 350 ms after editing. Turn it off to use Calculate or Ctrl/Cmd + Enter. Edits disable export immediately; Example and Clear show changes before applying them, and Undo restores both the inputs and report.
Compare signed calendar days with elapsed hours, minutes and seconds in a named timezone. Reversing the two endpoints keeps a negative difference instead of silently exchanging them.
Use a positive or negative integer to move by calendar days, or select elapsed hours for a fixed duration. Calendar-day arithmetic preserves the local clock time when that time exists uniquely at the destination.
Count whole working dates using any set of weekend weekdays, including no weekends or all seven days. A holiday list only removes dates: it cannot turn a scheduled weekend into a makeup workday.
Inspect the week number together with its week year, weekday, day of year, leap-year flag and month/year lengths. January 1, 2021 belongs to ISO week 53 of 2020, even though its calendar year is 2021.
Enter a birth date and a date to measure against. The result contains completed anniversary years, remaining calendar months and days, plus total days; it does not assume that the reference date is today.
Yes. Gregorian leap years are divisible by four, except century years unless divisible by 400. Thus 2000 is a leap year and 1900 is not. Date information reports the leap-year flag and 365 or 366 days; invalid February dates are rejected.
A difference measures the boundary between dates: Monday to Tuesday is one day. Counting both dates means two calendar days. Use the endpoint switch for that inclusive count. In business mode the additional end date must also qualify as a working day.
Day additions cross real calendar month boundaries; a day is never approximated as one thirtieth of a month. Age counts completed calendar years and then months, constraining an anniversary at month end where needed. Add mode deliberately has no month or year unit.
Yes, when a timed mode uses an IANA zone. The spring example in New York gives one calendar day and 23 hours. An explicit input offset identifies an instant; without one, repeated or missing local times produce an error. Date-only business and age modes do not interpret clocks.
The tool has no built-in public-holiday calendar. Add the relevant full date to the holiday list and check your weekend selection. A holiday outside the interval, on an excluded weekend or repeated in the list does not remove an additional day.
A result needs a closer look?
Use the date calculator with a known example, confirm the clock and endpoint rules, then keep the report alongside your calculation.