01
Calendar difference
Expresses the interval in complete years, complete months, and remaining days.
Date and time tool
All CalculatorsDate Difference Calculator
Calculate the exact interval between two dates in years, months, weeks, days, weekdays, and other useful formats.
Interactive calculator
Enter two calendar dates
Select a start date and an end date. The calculator will display several ways of describing the interval.
Select two dates
Your exact date difference and supporting results will appear here.
How do you calculate the difference between two dates?
The difference between two dates can be expressed as the total number of elapsed days or as a calendar interval in years, months, and days. Total days are calculated from the elapsed time between the two calendar dates. Calendar units are calculated by advancing from the earlier date in complete years and months before counting the remaining days.
Total-day formulaDate difference = Later date − Earlier date
The result is divided by the number of milliseconds in one day when dates are processed programmatically.
Worked example
From January 1 to January 10
The dates are nine elapsed days apart when the starting day is excluded. Counting both January 1 and January 10 produces an inclusive count of ten calendar dates.
StartJanuary 1
Elapsed difference9 days
Inclusive count10 days
January 1January 10
Nine complete 24-hour intervals separate the two dates.
Understanding results
Different ways to measure a date interval
A single interval can be described in several valid ways. The most useful result depends on the purpose of the calculation.
02
Total days
Counts every complete elapsed day between the earlier and later dates.
03
Weeks and days
Divides the total day difference into complete seven-day periods and a remainder.
04
Business days
Counts weekdays while excluding Saturdays and Sundays. Public holidays are not automatically excluded.
Calendar structure
Why months cannot all be treated as equal lengths
Calendar months contain 28, 29, 30, or 31 days. Because their lengths vary, a calendar result such as “one month” is not always equivalent to a fixed number of elapsed days.
The exact calendar difference therefore advances through complete months rather than dividing the total days by 30.
February28 or 29 days
April30 days
January31 days
Counting methods
Exclusive and inclusive date differences
Starting date is not counted
This measures elapsed time. From Monday to Tuesday, the difference is one day.
January 1 to January 10 = 9 daysBoth boundary dates are counted
This counts calendar dates touched by the interval. It is often used for schedules and attendance periods.
January 1 through January 10 = 10 daysBusiness-day counting
Calendar days vs weekdays
Calendar days include every day of the week. Weekdays include Monday through Friday and exclude Saturday and Sunday. The calculator does not exclude national or local public holidays because holiday calendars differ by country and region.
MonCounted
TueCounted
WedCounted
ThuCounted
FriCounted
SatWeekend
SunWeekend
Leap-year effect
How February 29 changes a date difference
A leap year contains 366 days instead of 365. When an interval crosses February 29, the total day count may include one additional day. The calculator counts every actual calendar day, including leap days.
February 28
→February 29Leap day
→March 1
Manual calculation
How to subtract two dates manually
- 1Place the later date above the earlier date
Confirm which date comes first before beginning the subtraction.
- 2Subtract the day values
Borrow the number of days in the previous month when the later day value is smaller.
- 3Subtract the month values
Borrow one year as 12 months when necessary.
- 4Subtract the years
The result is the calendar interval in years, months, and days.
Common mistakes
Errors to avoid when comparing dates
Decide whether you need elapsed days or an inclusive count before using the result.
Calendar months have different lengths, so fixed 30-day division is only an approximation.
An interval crossing February 29 can contain an additional elapsed day.
A true business-day result may also need to exclude official holidays.
Detailed guides
Learn more about date differences
Use these guides for formulas, manual methods, examples, calendar rules, and different counting conventions.
01How to Calculate the Difference Between Two Dates
Learn the complete process for measuring the interval between calendar dates.
Read guide →02How Many Days Are Between Two Dates?Count elapsed days and understand inclusive and exclusive results.
Read guide →03How to Calculate Weeks Between Two DatesConvert a date interval into complete weeks and remaining days.
Read guide →04How to Calculate Months Between Two DatesCompare complete calendar months with approximate month totals.
Read guide →05Years, Months, and Days Between Two DatesBreak a date interval into a calendar-based combination of units.
Read guide →06Calendar Days vs Business DaysUnderstand the difference between all days and working days.
Read guide →07How to Calculate Business Days Between Two DatesCount weekdays while excluding Saturdays and Sundays.
Read guide →08Inclusive vs Exclusive Date CountingSee when the starting date should or should not be counted.
Read guide →09How Leap Years Affect Date DifferencesLearn when February 29 adds an extra day to an interval.
Read guide →10How to Subtract Dates ManuallyWork through date subtraction without relying on software.
Read guide →Frequently asked questions
Date Difference Calculator FAQs
How many days are between two dates?
Subtract the earlier date from the later date. The calculator reports the number of complete elapsed calendar days between them.
Does the calculator count the starting day?
The standard total-day result excludes the starting day because it measures elapsed time. Select the inclusive option to count both dates.
How are years, months, and days calculated?
The calculator advances through complete calendar years and months from the earlier date, then counts the remaining days.
Are weekends included?
Weekends are included in total calendar days. They are shown separately from the weekday count.
Are public holidays excluded?
No. Holiday rules vary by location, so the weekday result excludes Saturdays and Sundays only.
Can the dates be entered in either order?
Yes. The calculator identifies the earlier and later date and reports the direction of the interval.
How are leap years handled?
Every real calendar day is counted. An interval that crosses February 29 includes the leap day.
Why is one month not always 30 days?
Calendar months contain between 28 and 31 days. Exact calendar-month results therefore use month boundaries rather than a fixed 30-day conversion.
Calculate another interval
Use the calculatorCompare any two calendar dates
Return to the calculator to view the exact calendar difference, total days, weeks, weekdays, weekends, and leap-day information.