About the Add or Subtract Time From a Date
Working out a date a certain time before or after another, a deadline 45 days out, a renewal a year on, a delivery in 10 business days, is easy to get wrong by hand around month ends. This tool does it correctly: enter a start date, choose to add or subtract, and set the amount and unit. Month and year arithmetic is calendar-aware, and the business-day option skips weekends.
Month arithmetic is where tools quietly disagree with each other. Adding one month to 31 January cannot produce 31 February, so the result is clamped to the last valid day of the target month: 28 February, or 29 in a leap year. The consequence catches people out, because the operation stops being reversible. Add a month to 31 January and subtract a month from the answer and you land on 28 January, not the 31st. When an exact interval matters, such as a contractual notice period, count in days or weeks instead, since those never need clamping.
The result is shown in full, with the weekday and relative phrasing, so you can confirm it. Dates can be in almost any format or a timestamp; "now" uses the current moment. Typical questions it settles are when an invoice due 45 days out actually falls, which day a 14-day trial ends, and what date a delivery quoted as 10 business days lands on. To find the gap between two dates instead, use the Date Difference Calculator; to see the resulting month laid out, the Monthly Calendar Generator.
How to use
- Enter the start date in the pane.
- Choose add or subtract, the amount and the unit.
- Read the resulting date.
Common questions
- How is adding a month handled around month end?
- Calendar-aware: adding a month to 31 Jan gives the end of February, since there is no 31st.
- What do business days skip?
- Saturdays and Sundays. Public holidays are not accounted for.
- Can I use it from today?
- Enter "now" as the start date to calculate from the current moment.