Date Difference Calculator
Calculate days, weeks, months, and years between two dates. Useful for project timelines, deadlines, and tracking events.
Select Dates
How Date Difference Is Calculated
Days = |End Date − Start Date| ÷ (1000 × 60 × 60 × 24)
The calculator takes the absolute difference between two dates in milliseconds and converts to days. Weeks (÷ 7), months (÷ 30.44), and years (÷ 365.25) are derived from the day count. The 365.25 divisor accounts for leap years (one extra day every 4 years).
Example
From January 1, 2026 to August 22, 2026:
How to Interpret Your Result
- Months and years are approximate: Because months have 28-31 days, the ÷ 30.44 and ÷ 365.25 conversions are averages. For exact calendar months, count the month boundaries instead.
- The day count is exclusive of one endpoint: From Jan 1 to Jan 2 is 1 day, not 2. If you need inclusive counting (both start and end days), add 1 to the result.
- Use cases: Project deadlines (days remaining), age in days (see the Age Calculator or Life Days Calculator), contract durations, and event planning.
Common Mistakes
- Inclusive vs exclusive counting: "How many days from Monday to Friday?" — the calculator returns 4 (exclusive). If you mean "including both Monday and Friday," the answer is 5.
- Ignoring leap years: A 1-year span crossing Feb 29 has 366 days, not 365. The calculator handles this automatically via the millisecond calculation.
- Timezone drift: The dates are treated as midnight local time. If your dates span timezones, the day count may be off by one in edge cases.
Frequently Asked Questions
How do I calculate days between two dates?
Enter the start and end dates. The calculator counts the total days, then converts to weeks, months, and years.
Does this calculator include weekends?
By default it counts all days (including weekends). You can also filter to count only business days.
What can I use this for?
Common uses: counting days until a deadline, tracking project timelines, calculating age in days, or finding days between events.