Date & Time
Date Calculator
Measure the gap between two calendar dates or add/subtract a custom number of days from a starting point.
Add/subtract days or measure the gap between dates.
Date arithmetic
The calculator converts each date into an absolute timestamp, finds the difference in milliseconds, and then expresses the gap in days and weeks. For add/subtract modes it offsets the start date by the requested number of days.
How to use
- Choose the mode: difference, add days, or subtract days.
- Fill in the start date and either the end date or number of days depending on the mode.
- Check the results for total days, weekly equivalent, or the resulting calendar date.
Example
Input: Mode = Difference, Start date = 2024-01-01, End date = 2024-03-15
Output: Days between = 74 (≈10.57 weeks)
FAQ & notes
Does the tool account for leap years?
Yes. It uses native JavaScript date math, so leap days are included automatically when a range spans February 29.
Can I add business days only?
This calculator works with calendar days. For business-day schedules, convert your target into calendar days before using the tool.