Date CalculatorFree online other calculator — instant results, no sign-up
Add or subtract days from a date.
Sign in to save results and favorites.
How the result changes with days to add (negative to subtract)
Each row below was calculated with this tool, keeping every other input at its default and changing only days to add (negative to subtract) from half to one and a half times the default value. Use it to see how sensitive the answer is before you enter your own numbers.
| Days to add (negative to subtract) | Result |
|---|---|
| 45 | Sun, February 15, 1970 |
| 68 | Tue, March 10, 1970 |
| 90 (default) | Wed, April 1, 1970 |
| 113 | Fri, April 24, 1970 |
| 135 | Sat, May 16, 1970 |
About the Date Calculator
The Date Calculator determines a future or past calendar date by adding or subtracting an exact number of days from a selected starting point. It is commonly used for scheduling deadlines, tracking warranty expirations, managing project milestones, or planning legal and contractual response periods.
- Start date
- The initial reference date in YYYY-MM-DD calendar format.
- Days to add (negative to subtract)
- An integer representing the number of consecutive calendar days to advance forward (positive) or roll backward (negative).
Formula and method
Target Date = Start Date + k days
- Target DateThe resulting calendar date after shifting by the specified day count
- Start DateThe baseline calendar day from which counting begins
- kNumber of full calendar days added (if positive) or subtracted (if negative)
The tool parses the start date in standard Gregorian calendar time and adjusts the calendar day count by the signed integer value entered. It accounts for varying month lengths (28 to 31 days) as well as leap years, formatting the resulting date with the weekday, month name, day, and year.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Start date1970-01-01
- Days to add (negative to subtract)90
Results
- ResultWed, April 1, 1970
How to use the Date Calculator
- 1Select or enter the initial calendar date.
- 2Enter the number of calendar days to count forward, or enter a negative value to count backward.
- 3Advance or rewind the calendar month by month, taking into account varying month lengths and leap years.
- 4Read the final calculated day of the week and date.
Reading your result
The primary result displays the exact day of the week and full date that occurs after adding or subtracting the specified days. This shows the continuous calendar day point, including weekends and statutory holidays.
Limitations
This calculator counts elapsed calendar days continuously; it does not skip weekends or public holidays to compute business days. It also assumes the standard Gregorian calendar throughout and does not account for time-of-day offsets or daylight saving time shifts.
Common questions
Does adding days include or exclude the start date?+
Adding days counts forward from the start date, meaning day 1 is the next calendar day. For example, adding 1 day to a Monday lands on Tuesday.
How does the calculator handle leap years?+
The underlying date arithmetic automatically identifies leap years and inserts February 29 when the counted range spans across that date.
Can I calculate business or working days with this tool?+
No, this calculator counts every consecutive calendar day. To track business days, you must manually adjust for the intervening weekend days and relevant public holidays.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
Further reading
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Results are estimates for informational purposes and are not financial, medical or legal advice.