Free Online Date Difference Calculator
Calculate the exact number of days, weeks, months, and years between any two dates.
Select both dates to see the difference
How Date Difference Calculation Works
Calculating the difference between two dates seems simple until you consider the irregularities of our calendar system. Months have 28, 29, 30, or 31 days. Years have 365 or 366 days. Time zones can shift dates. And "one month from January 31" is ambiguous — is it February 28, March 1, or March 3?
This calculator uses a straightforward approach: it counts the actual calendar days between two dates, then converts to weeks, months, and years. For months, it uses calendar months (Jan 15 to Feb 15 = 1 month, regardless of whether that's 31 or 28 days). For years, it uses full calendar years.
Leap years are handled correctly — February 29 exists in years divisible by 4, except centuries not divisible by 400. So 2024 is a leap year, 2100 is not, but 2000 was. The calculator accounts for all of this automatically.
Business days exclude weekends (Saturday and Sunday) but don't account for public holidays, which vary by country and region. For precise business day calculations involving holidays, you'd need a country-specific holiday calendar.
When You Need Date Calculations
Counting days until an event
How many days until your wedding, vacation, or deadline? Enter today and the target date to get an exact countdown in days, weeks, and months.
Calculating project timelines
If a project started March 15 and the deadline is September 30, how many business days do you have? This helps with sprint planning, resource allocation, and deadline negotiations.
Determining age or duration precisely
How many days old are you? How long have you been at your job? How many days since a historical event? Get exact numbers instead of rough estimates.
Contract and legal date calculations
Leases, warranties, and legal deadlines often specify "30 days," "90 days," or "6 months." Calculate the exact end date from a start date to avoid missing deadlines.
Date Calculation Tips
Business days vs calendar days matter for deadlines
"30 days" in a legal context usually means calendar days. "30 business days" excludes weekends and is actually about 6 weeks. Always clarify which type of days a deadline refers to — the difference can be significant.
Month calculations can be ambiguous
"One month from January 31" could be February 28 or March 3 depending on interpretation. This calculator uses the convention that one month later means the same day number in the next month (or the last day if that day doesn't exist).
Time zones can shift dates
If you're calculating across time zones, a date in one zone might be a different date in another. This calculator works with dates only (not times), so it gives consistent results regardless of your time zone.
Features
- Calculate difference in days, weeks, months, and years
- Business days calculation (excludes weekends)
- Add or subtract days from a date
- Handles leap years correctly
- Shows results in multiple units simultaneously
- Works with any date range — past or future
- No signup required — instant results
Frequently Asked Questions
Does it account for leap years?
Yes. The calculator correctly handles leap years (years divisible by 4, except centuries not divisible by 400). February 29 is included in day counts when it falls within your date range. A year from Feb 29, 2024 is Feb 28, 2025.
How are business days calculated?
Business days count only Monday through Friday, excluding Saturday and Sunday. Public holidays are not excluded because they vary by country and region. For a rough estimate, business days are approximately 5/7 (71%) of calendar days.
Can I add days to a date?
Yes. Enter a start date and the number of days (or weeks/months) to add, and the calculator will show the resulting date. This works for both adding and subtracting — useful for calculating deadlines, due dates, or past dates.
How does it handle months with different lengths?
When adding months, the calculator moves to the same day in the target month. If that day doesn't exist (e.g., adding 1 month to January 31 → February doesn't have 31 days), it uses the last day of the target month (February 28 or 29).
What's the maximum date range supported?
The calculator supports any date that JavaScript can represent — roughly from year 271,821 BCE to year 275,760 CE. For practical purposes, any date you'd reasonably need to calculate is supported.
Tips & Related Workflows
- Calculate someone's exact age with our Age Calculator.
- Convert Unix timestamps to readable dates with our Timestamp Converter.
- Convert between time units (hours, minutes, seconds) with our Unit Converter.