What is Date Calculator?
A Date Calculator computes the exact calendar duration between two dates or projects a target date forward/backward by adding or subtracting time units.
How to Use Date Calculator
- 1Select mode: "Difference Between Dates" or "Add/Subtract Days".
- 2In Difference mode, pick Start Date and End Date to see total days, weeks, and months elapsed.
- 3In Add/Subtract mode, pick Start Date, select operation (+ or -), and enter number of days/months/years.
- 4View the projected final date instantly.
How Does Date Calculator Work?
Uses UNIX timestamp delta calculation converted to UTC calendar units to avoid DST shifts.
Date Difference = |Target Date Timestamp − Start Date Timestamp| / 86,400,000 msPractical Examples
Project Deadline Projection
Start Date: October 1, 2026. Add 90 days.
Frequently Asked Questions
Does this calculator exclude weekends or holidays?
By default, the date calculator computes total calendar days. You can also view total business days (Monday–Friday count).
How are leap years calculated when adding years?
If starting on February 29 of a leap year and adding 1 non-leap year, the result lands on February 28.
Can I calculate negative date differences?
Yes, if the end date occurs before the start date, the tool indicates a negative interval.
Does Daylight Saving Time (DST) affect the day count?
No. The calculator normalizes calculations at 00:00:00 UTC, preventing 23-hour or 25-hour DST clock shifts from skewing day totals.
What is the maximum date range supported?
Our tool supports dates spanning from year 100 AD to year 9999 AD.