A 90-day deadline
Starting on Tuesday, 3 November 2026 and adding 90 days gives Monday, 1 February 2027. The offset is +90 days. The weekday moved back one place because 90 days is 12 weeks and 6 days.
Add Days to a Date or Subtract Days
Add days to a date or subtract days from it to find the resulting calendar date and its day of the week. Month lengths and leap years are handled for you.
Date and days
Defaults to today. Pick any date from year 1 to 9999.
A whole number from 0 to 1,000,000.
Quick picks:
Pick a date
Choose a starting date and the number of days to see the resulting date.
How to use the Add or Subtract Days
- Choose Add days to move forward or Subtract days to move back.
- Pick the starting date. It begins as today, and you can change it to any date from year 1 to 9999.
- Type the number of days, from 0 to 1,000,000, or tap a quick pick such as 30 days or 90 days.
- Read the resulting date with its weekday, together with your original date and the signed offset.
- Press Copy result to copy a one-line sentence, or Reset to return to today and 30 days.
How days are added to or subtracted from a date
Every calendar date is converted to a single running day number, the number of days since 1 January 1970. Adding or subtracting is then plain arithmetic on that number, and the result is converted back to a day, month and year. That is why month lengths, year ends and leap days all come out right without any special cases. Adding 365 days to Thursday, 29 February 2024 gives Friday, 28 February 2025, because 2025 has no leap day.
The weekday comes from the same day number, because the days of the week repeat every 7 days. A shift that is a multiple of 7 always lands on the same weekday.
Days are counted as whole calendar days. The starting day is day 0, so adding 1 day to Monday gives Tuesday. If the answer would fall before year 1 or after year 9999, the tool reports an error instead of showing a wrong date.
Result = start date + N days (add) or start date - N days (subtract) Signed offset = +N when adding, -N when subtracting Weekday moves forward by (N mod 7) places when adding, back by (N mod 7) places when subtracting
- To count the days between two dates you already have, use the Days Between Dates.
- To see the gap as weeks, months and years too, use the Date Difference Calculator.
Assumptions and limits
- Adds or subtracts whole calendar days. Time of day, time zones and daylight saving changes are not considered.
- Weekends and holidays are counted as ordinary days.
- Leap years follow the Gregorian rules for every year, including years before the calendar was adopted. Supported years are 1 to 9999.
Practical examples
Looking back 100 days
Subtracting 100 days from Tuesday, 3 November 2026 gives Sunday, 26 July 2026, an offset of -100 days.
30 days is not the same as one month
Adding 30 days to 31 January 2026 gives Monday, 2 March 2026. One calendar month after 31 January would be the end of February, so a month and 30 days differ when month lengths differ.
Frequently asked questions
How do I add days to a date?
Choose Add days, pick the starting date (it begins as today), then type the number of days or tap a quick pick. The new date and its weekday appear immediately.
Is the starting day counted as day 1?
No. The starting day is day 0, so adding 1 day gives the next calendar day. If your deadline rule says to count the first day as day 1, add one day fewer.
Does it skip weekends or public holidays?
No. It adds calendar days, so weekends and holidays count like any other day. This tool does not calculate working days.
How is this different from adding months?
Months have different lengths, so adding 30 days is usually not the same as adding one month. This tool only moves by an exact number of days.
Why is there a limit of 1,000,000 days?
It keeps the input sensible. 1,000,000 days is roughly 2,738 years, which is already far longer than any real planning period. For example, adding it to 3 November 2026 gives Wednesday, 30 September 4764.
What happens near the first or last supported year?
Dates from 1 January of year 1 to 31 December of year 9999 are supported. If your result would leave that range, you get a clear error and no date.