21 days from today

Months and years are added calendar-wise, keeping the same day of the month whenever it exists. If it does not, the result is clamped to the last day of that month: 31 January plus one month is 28 February, or 29 February in a leap year, rather than spilling over into March.

No. The tool counts full days after the start date, so 30 days from Monday 5 October is Wednesday 4 November. If a rule says the first day counts as day one, as many return policies and Korean 100-day celebrations do, subtract one day from the result or enter one day less.

Four weeks is always exactly 28 days. One month moves the calendar month forward and keeps the same day number, so it can be 28, 29, 30 or 31 days long. For pay periods and subscriptions check which rule the contract uses before relying on either figure.

Days are counted on the real calendar, so 29 February is included in leap years such as 2028. Daylight-saving changes do not affect the result because the tool works with whole calendar dates, not hours, which is why the days-from-start figure is always a whole number.

Yes. Choose "Subtract" to move backwards, for example 90 days before a court date or 18 months before today. The days-from-start figure is always shown as a positive number, and the weekday tells you whether the date fell on a weekend.