Date Calculator
Use this when you need the date a set period before or after another date — a 30-day deadline, a 90-day return window or a six-month review.
How it works
- Days and weeks are added as fixed amounts: one week is always seven days.
- Months and years shift the calendar position instead of adding a fixed day count, because months differ in length.
- When the original day number does not exist in the target month, the result is clamped to that month's last day.
Notes
- January 31 plus one month gives February 28, or February 29 in a leap year.
- Leap days are counted automatically when adding days across February.
Common questions
- Why is January 31 plus one month not March 3?
- Adding a month means moving to the same day number in the next month. February has no 31st, so the result is clamped to the last day of February — the convention used by contracts and most software.
- Does it count the start date?
- No. Adding 1 day to March 1 gives March 2. If you need to count both endpoints of a range, use the Days Between Dates Calculator, which shows inclusive and exclusive totals.