Add or Subtract Days from a Date
Start from any date, choose to add or subtract, enter an amount of days, weeks, or months, and see the resulting calendar date along with its day of the week. This answers questions like "what date is 90 days from today?", "when does my 30-day return window end?", or "what was the date 6 weeks ago?".
Counting forward by hand goes wrong at month boundaries and leap years. The calculator works on the real calendar, so adding a month to 31 January correctly lands on the last day of February, and day arithmetic across leap years stays exact.
How it's calculated
Result = start date ± N days (or N × 7 days, or N calendar months)
Days and weeks are exact arithmetic on the calendar. Adding months moves the same day-of-month forward; when the target month is shorter, the result clamps to its last day (31 Jan + 1 month = 28/29 Feb).
Worked example
90 days after 30 August 2026 is 28 November 2026, a Saturday. A 30-day return window on a purchase made 15 August ends on 14 September. Six weeks before 1 October 2026 is 20 August 2026.
Frequently asked questions
›What date is 30/60/90 days from today?
Enter today's date and add 30, 60, or 90 days. These spans are common for invoices (net-30/60/90), probation periods, and return policies. The result shows the weekday too, since deadlines landing on weekends often roll to the next business day.
›How is adding a month different from adding 30 days?
Adding a calendar month keeps the same day number (15 March + 1 month = 15 April), while adding 30 days counts exactly 30 days regardless of month length. Contracts usually mean calendar months.
›What happens when the result month is shorter?
The date clamps to the month's last day: 31 January plus one month gives 28 February (29 in a leap year). This matches how most legal and billing systems handle it.
›Can I subtract into the past?
Yes. Switch to subtract to answer questions like "what date was 45 days ago?", useful for backdating logs or checking when a notice period must have started.
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