Add days to a date
What date is 30, 60 or 90 days from a given day — with the weekday it lands on and its ISO week number, so you can tell straight away whether it falls at a weekend.
Add or subtract days and weeks
The 30, 60, 90 rhythm
Invoice terms, notice periods, probation and follow-ups almost all run in thirties, and none of them care what day of the week the result lands on. That is what makes the weekday worth showing: a 90-day payment term that ends on a Saturday is effectively due on the Friday or the Monday, depending on whose rules you follow.
Months are not 30 days
"Three months" and "90 days" agree only by accident. From 1 January, 90 days lands on 1 April in a common year and 31 March in a leap year — and three calendar months always land on 1 April. If a contract says days, count days; if it says months, count months. The mismatch is where disputes start.
Counting backwards
Switch the direction to earlier to work back from a fixed date: 60 days before a launch, 14 days before a deadline, the last day notice can be given. The result is the same arithmetic in reverse, and the weekday matters just as much.
Questions
Does adding days skip weekends?
No — this tool adds calendar days, so the result can land on a Saturday, and it says when it does. To count in working days instead, use the business days calculator.
What is the largest number of days I can add?
100,000 days, which is around 273 years. Dates outside that range say more about the calendar system than about anything you are planning.