This date calculator adds or subtracts calendar time and counts between dates with explicit endpoint rules.
Calendar arithmetic with clear counting rules
Choose the calendar job before entering dates. Add or subtract from a date finds a new date from your entered calendar units. between two dates reports a signed count and lets you choose the boundary convention. Optional , and stay behind the larger-unit control. Every calculation follows the same Gregorian calendar basis, so changing a device time zone does not alter an entered-date result.
Calendar offsets include weekends. counts between dates use the selected endpoint convention.
Unavailable target dates are constrained to the last valid date of the target month, before any extra movement.
Month-end date worked example
Start with January 31, 2025 and add 1 with 0 extra . The result is February 28, 2025, Friday. The elapsed gap is 28 . The date is constrained to the last valid date of the target month.
Adding 1 further after that month shift gives March 1, 2025. Larger calendar units are applied before the smaller date shifts; they are not converted into an average number of .
Elapsed days and inclusive date ranges
The elapsed gap counts calendar steps from start to end. Including both boundary dates adds a date to the magnitude; excluding both removes a date, with a minimum of zero. Reversing unequal dates reverses the sign. An inclusive range consisting of a single date contains that one date.
From January 1 to January 4, 2025, Include both dates returns 4 . From February 28 to March 1, 2024, Elapsed gap returns 2 , because that interval crosses . Reversing March 1 and February 28, 2025 gives -1 . The calendar period and whole details always describe the unadjusted elapsed span, separately from an inclusive or exclusive date count.
For a clock-based duration, use the Time Duration Calculator. It answers a different question from counting dates on a calendar.
Calendar months, leap years and time zones
A Gregorian is leap if its number is divisible by 4, unless it is divisible by 100 without also being divisible by 400. Month lengths follow the calendar. In the offset form, and are combined into one signed month shift and the starting date is constrained once. and are applied afterward. All entered counts are nonnegative whole numbers; Direction applies to the whole movement.
The example adds 1 to February 29, 2024 and returns February 28, 2025. Subtracting 90 from April 1, 2025 returns January 1, 2025. Constraining a month end can make reversing an offset land on a different date in the original month.
The elapsed calendar-period detail works chronologically from the earlier date: take the largest constrained whole-month shift that does not pass the later date, then count remaining . It is a declared reporting convention, not a legal anniversary rule. Historical dates use Gregorian rules throughout, without switching calendars at a country's historical reform. Supported inputs and resulting dates run from 0001 through 9999. Calendar dates do not identify a time zone or promise elapsed hours across clock changes.
When a weekly work schedule and closure dates determine which dates count, use the Business Days Calculator. It counts eligible calendar dates without turning them into paid work hours.
When a report needs an label, the Week Number Calculator returns the , number and weekday, and converts that identity back to a calendar date.