Date Calculator
Add or subtract days from any date to find the resulting calendar date.
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Quick Tip
Pick the start date.
About This Tool
Why use Date Calculator?
Add or subtract days from any date to find the resulting calendar date. The tool shows the target date, its day of the week, the duration expressed in weeks and days, and the ISO format (YYYY-MM-DD) that spreadsheets and databases expect.
This is the quickest way to answer deadline questions: 90 days from 15 January 2026 is 15 April 2026, a Wednesday. Enter a negative number to count backwards. Note that the count is in calendar days, so weekends and public holidays are included.
Key Benefits
Day of the week included
Knowing a deadline lands on a Saturday usually changes the plan, so it is shown with the date.
Forward and backward
Negative day counts subtract, which answers "what date was 45 days ago?".
ISO output
YYYY-MM-DD is provided for spreadsheets, databases and forms that require it.
How to use Date Calculator
- 1
Pick the start date.
- 2
Enter the number of days to add, or a negative number to go back.
- 3
Read the resulting date and the day of the week it falls on.
- 4
Copy the ISO format when you need the date in a spreadsheet or a form.
Best use cases
Find a 30, 60 or 90-day payment deadline.
Work out a notice period end date.
Count forward to a delivery or expiry date.
Check what date a course or trial started, counting back from today.
Date Calculator FAQs
Does this count working days or calendar days?
Calendar days, including weekends and holidays. For working days, count five per week and add the weekends back manually.
How do I count backwards from a date?
Enter a negative number of days. Subtracting 30 from 10 March 2026 gives 8 February 2026.
Does it handle leap years?
Yes. Real calendar arithmetic is used, so a range covering 29 February is counted correctly.
Is the deadline counted from the start date or the day after?
Adding 30 days gives the date 30 days later, so the start date itself is not counted. Contracts vary on this, so check the wording of yours.
Related Everyday Tools
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