Date Calculator
Calculate duration between two dates or add/subtract days from a date
Duration Between Dates
Add / Subtract Days
Result
How to Use This Calculator
- Select Duration Between Dates to measure the distance in days, weeks, or years between two calendar dates.
- Select Add / Subtract Days to project future or past calendar dates from a starting point.
- Input your starting and ending calendar dates using the date picker controls.
- Click “Calculate Date” to see exact calendar results.
The Logic Used
Calendar calculations account for varying month lengths and leap year intervals based on the Gregorian calendar standard:
Duration = (End Date – Start Date) in Milliseconds / (1000 × 60 × 60 × 24)
Target Date = Start Date ± (Days Count × 86,400,000 ms)
Target Date = Start Date ± (Days Count × 86,400,000 ms)
Frequently Asked Questions (FAQ)
Does this calculator account for leap years?
Yes, calculations rely on full UTC epoch timestamps, accounting for 29-day Februaries in leap years.
How many days are in a standard calendar year?
A standard calendar year contains 365 days, whereas leap years occur every 4 years and contain 366 days.
What is epoch time in computing?
Unix epoch time measures the number of seconds that have elapsed since midnight on January 1, 1970 (UTC).
How many weeks are in one calendar year?
A standard calendar year contains 52 weeks plus 1 day (or 2 days during leap years).
Can I calculate business days with this tool?
This tool measures total consecutive calendar days including weekends and statutory public holidays.