What Is a Date Calculator?
A date calculator finds the number of days between two dates, or lets you add or subtract a number of days from a starting date to find a new date — useful for deadlines, project planning, or scheduling.
How to Use the Date Calculator
- Choose "Days Between Dates" or "Add / Subtract Days" mode.
- Enter your dates (or a starting date and number of days).
- View your result instantly, including a weekday breakdown.
Date Calculation Method
For date differences, the calculator counts full calendar days between the two dates. For adding or subtracting days, it moves forward or backward the specified number of calendar days from your starting date, correctly rolling over month and year boundaries and accounting for leap years.
Worked Example
From: January 1
To: March 15
Result: 73 days apart (accounting for the actual number of days in January and February).
Understanding Your Results
In "Days Between" mode, you'll see the total day count plus a weeks-and-days breakdown, and how many of those days were weekdays versus weekend days — useful for estimating business-day deadlines. In "Add/Subtract" mode, you'll see the resulting calendar date.
Common Mistakes to Avoid
- Confusing calendar days with business days — check the weekday breakdown if you need working days specifically.
- Forgetting that "days between" is typically an exclusive count of the start date but inclusive of the end date — always verify which convention your use case needs.
Frequently Asked Questions
Enter both dates in 'Days Between Dates' mode — the calculator subtracts one date from the other and shows the exact day count, including a weekday/weekend breakdown.
Switch to 'Add / Subtract Days' mode, set the starting date to today, and enter 90 in the days field.
Yes — it uses standard calendar date arithmetic, which automatically accounts for leap years and varying month lengths.
Yes — enter a negative number in the 'Days to Add' field to move backward from your starting date.
Calendar days count every day including weekends. Business (weekday) days exclude Saturdays and Sundays — the calculator shows both breakdowns in 'Days Between' mode.