Date add and subtract calculator
Choose a start date, an operation and a duration. The result shows the new date and weekday. Days and weeks use calendar arithmetic. For months, a missing day is adjusted to the last day of the target month.
Calculate a new date
How months are calculated
Adding a month keeps the day number when it exists in the target month. Otherwise, the result is the last day of that month. For example, one month after January 31 is February 28 or 29. Leap years are handled.
Dates and deadlines: check the applicable rule
This tool performs calendar arithmetic. It does not calculate business days, public holidays, cutoff times or legal and contractual counting rules. The starting point and whether the first day is included vary by context. Check the relevant organization’s instructions or contract before treating a result as an official deadline.
Frequently asked questions
Are weeks counted as business days?
No. A week is seven calendar days. Weekends and public holidays are not removed.
What does adding one month to January 31 do?
February has no day 31, so the result is the last day of February: the 28th or 29th.
Does the calculator move a date that falls on a weekend?
No. It shows the calculated date. Some rules may move a deadline, depending on the context and location.
Is the starting day included in a deadline count?
This tool adds or subtracts calendar time. Official deadline-counting conventions can differ; follow the rule that applies.