Date Add/Subtract Calculator

Add or subtract years, months, weeks, and days simultaneously. Support for business days and holidays exclusion.

Timeline Settings

Start Date

Operation

Time Intervals Offset

Years

Months

Weeks

Days

Business Days Settings

Provide start date and timeline values.

How calendar date arithmetic is calculated

Standard date arithmetic adjusts calendar indexes sequentially. Adding months or years accounts for varying length of months and leap years by clamping final results to standard boundary days (e.g. adding 1 month to January 31 results in February 28 or 29).

Business day selectors implement skipped iterations, bypassing weekend boundaries (Saturdays and Sundays) and standard US federal holidays (such as Memorial Day, Labor Day, and Thanksgiving) to calculate exact work schedule projections.

Built and maintained by Meet Shah · Last updated 1 August 2026

What this tool is used for

Adding a notice period to a date to find the end date.
Working out a date thirty days from now.
Subtracting months from a date for a retrospective window.
Finding a date a set number of weeks ahead without counting on a calendar.
Checking a deadline someone else calculated.

Frequently Asked Questions

What happens when the target month is shorter?: The day is clamped: adding one month to 31 January gives 28 February, or 29 in a leap year. Every date library does this, and it means the operation is not reversible — subtracting a month from that result gives 28 January, not the 31st you started from.
Which days count as business days?: Monday to Friday, excluding weekends. US federal holidays are recognised, including Juneteenth, which only became a federal holiday in 2021 — so older tools and older spreadsheets quietly disagree with this one about mid-June dates.
Why does my contract deadline land differently?: Because "within 30 days" and "within 30 business days" are wildly different, and jurisdictions differ on whether the start date counts. Many legal texts say "clear days", which excludes both the first and last — check the wording before trusting any arithmetic.
Is a year always 365 days here?: No — adding a year moves the calendar year and keeps the month and day, so it is 366 days across a leap day. That is what people mean by "a year later", and it is why calendar arithmetic cannot be replaced by adding a fixed number of seconds.
Does daylight saving affect the result?: Not for whole-day arithmetic, which works on calendar fields rather than elapsed time. It very much affects durations in hours: the same "one day later" is 23 or 25 hours across a clock change, which is why a reminder set in hours drifts and one set in days does not.

Common errors and gotchas

Adding a month to 31 January and expecting a valid date, which conventions resolve differently.
Adding months then days rather than days then months, which can land on a different date.
Ignoring time zones, which can shift the result by a day.
Overlooking a daylight-saving transition when adding hours.
Assuming a month means 30 days, which no calendar month reliably is.