Date Calculator: Add, Subtract and Days Between Dates
Add time to a date, take time away from it, or find how many days lie between two dates.
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Date Calculator: Add, Subtract and Days Between Dates by TheCalcTools
How the Date Calculator works
Choose whether to add time, subtract time, or count the days between two dates. For adding or subtracting, pick the unit; for the difference, enter both dates.
Days and weeks are added exactly. Months and years keep the same day of the month where possible, and if that day does not exist (for example, 31 April or 30 February), the result moves to the last day of the month. The difference is shown in total days and also as years, months and days.
The formula
Worked example
Add 90 days to 10 October 2026:
| Start date | October 10, 2026 |
|---|---|
| Add | 90 days |
- October has 21 days left after the 10th, November 30 and December 31, which makes 82 days to 31 December.
- The remaining 8 days run into January, giving Friday, January 8, 2027.
- That is 90 days after the start date.
Result:
| Result | Friday, January 8, 2027 |
|---|---|
| Detail | 90 days after the start date |
Frequently asked questions
How many days are there between two dates?
Choose “Days between two dates” and enter both. The count is the difference in calendar days, not counting the start day itself.
How are months added?
The month moves forward and the day stays the same. If the new month is shorter, the date moves to its last day, so 31 January plus one month is 28 or 29 February.
Does this count weekends or holidays?
It counts all calendar days. For business days, use the working days calculator.
Can I find my exact age?
Yes, try the age calculator.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.