Date Difference & Days Between Dates Calculator
Easily determine the exact number of days, weeks, and months between any two calendar dates for project deadlines, milestone countdowns, or tenure tracking.
How it works
Calculates the absolute duration between timestamps and breaks it down into full elapsed calendar years, months, and remaining days.
Formula
Days = |End Time - Start Time| / 86,400,000 ms, Weeks = Days / 7
Computes the precise millisecond difference between two UTC calendar dates and converts into elapsed days, weeks, months, and calendar years.
| Symbol | Variable | Unit | Description |
|---|---|---|---|
| Time_start | Unix timestamp of start date | ms | |
| Time_end | Unix timestamp of end date | ms |
Worked example
Duration from 2026-01-01 to 2026-12-31
- Start Date:
- 2026-01-01
- End Date:
- 2026-12-31
Total days = 364 days (52.0 weeks / 12.0 months). Calendar breakdown: 0 years, 11 months, 30 days.
Limitations
Does not exclude public holidays or weekend non-working business days.
Frequently asked questions
Does the date difference calculator account for leap years?
Yes, standard JavaScript Date objects natively compute leap year days (such as February 29 in leap years like 2024 and 2028).
Is the end date included in the total days count?
This calculator measures the absolute time interval between the two dates (00:00 UTC to 00:00 UTC). If you need both start and end days inclusive, add +1 day to the result.
How is the calendar month breakdown calculated?
The calendar breakdown steps through whole Gregorian months and days, adjusting for variable month lengths (28, 30, or 31 days).
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Last reviewed: 2026-08-22.