Add or Subtract from a Date

When the source day does not exist in the target month (e.g. January 31 + 1 month) the calculator clamps to the last valid day of the target month — so January 31 + 1 month = February 28 (or 29 in leap years). This matches Go's standard time.AddDate behavior.

Yes. Enter a negative amount to count backwards. For example, today's date with -30 days returns the date 30 days ago. The unit field controls whether the negative count applies to days, weeks, months or years.

Adding 30 days always advances the date by exactly 30 calendar days. Adding 1 month advances to the same day-of-month in the next month, which can be 28, 29, 30 or 31 days depending on the month. Use days for fixed intervals (e.g. SLA deadlines) and months for calendar-based ones (e.g. monthly billing).

Yes. Adding 365 days to a date in a leap-year span will land one day earlier in the calendar than expected. Adding 1 year to February 29 lands on February 28 in non-leap years and back to February 29 in the next leap year.

The calculator uses Go's time package which supports dates from year 1 to year 9999. Practical use cases (project planning, historical research, future dating) easily fit within this range.

Project managers use it for milestone dates from a kickoff, lawyers use it for filing deadlines from a service date, parents use it to project due dates, and contract administrators use it for renewal anniversaries. Any time you need 'date X plus N units' precisely, this is the tool.