Date Difference Calculator
The Date Difference Calculator determines the amount of time between two calendar dates. It can be useful for project planning, event planning, contracts, milestones, anniversaries, schedules, and other situations where you need to know how far apart two dates are.
How to use this calculator
- Enter the first date.
- Enter the second date.
- Review the resulting interval.
- If the calculation is being used for an official deadline, verify whether the relevant rules count the starting date, ending date, weekends, holidays, or other special days.
Date difference methodology
Date difference = number of calendar days between the two specified dates.
- The calculator compares the two calendar dates rather than assuming every month contains the same number of days.
- The calculation therefore accounts for the actual length of each month and for leap years.
- Depending on the calculation convention, an interval can be expressed as elapsed days or broken into calendar years, months, and days.
Worked examples
Example: one-week interval
If one date is January 10 and another is January 17 of the same year, the dates are seven calendar days apart.
January 17 − January 10 = 7 days
The date difference is 7 days.
Example: crossing months
A period beginning late in one month and ending early in the next cannot be calculated reliably by simply subtracting the day numbers.
The calculator accounts for the actual number of days in both months.
Understanding the result
Date difference is not necessarily the same as an inclusive count. If both the starting and ending dates are counted as included days, the result can be one day larger.
Crossing a leap day changes the number of calendar days in the interval.
A calendar interval is different from an exact elapsed-time calculation when timestamps and time zones are involved.
Important notes
For legal or contractual calculations, follow the counting convention specified by the applicable agreement or authority.
Public holidays and weekends are not automatically the same as calendar days or working days.
If you need business-day calculations, use a method specifically designed for working days and the relevant holiday calendar.
Frequently asked questions
What is the difference between two dates?
It is the calendar interval separating the two dates. Depending on the context, the interval may be expressed in days or calendar units such as years, months, and days.
Does the date difference include both dates?
Not necessarily. A standard elapsed-day difference normally measures the interval between the dates. An inclusive day count treats one or both endpoints differently.
Do leap years affect date differences?
Yes. A leap year contains February 29, so intervals that cross that date can contain one additional calendar day.
Related calculators
- Date Calculator — Add or subtract years, months, weeks, and days from any date.
- Time Duration Calculator — Calculate elapsed time between two times using hours and minutes.
- Business Days Calculator — Count weekdays between two dates, excluding Saturdays and Sundays.
- Add & Subtract Time Calculator — Add or subtract hours and minutes to calculate a resulting time duration.
- Hours & Minutes Calculator — Add or subtract hours and minutes for work, study, travel, and everyday time calculations.
- Time Zone Converter — Convert times between any two time zones around the world.
Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
- How to Calculate Days Between Dates — Learn how date intervals work, including leap years and inclusive vs exclusive day counting.
- How to Calculate Age from a Date of Birth — Learn how exact age is calculated using years, months, and days rather than a rough year difference.
- Standard Deviation — Understand standard deviation as a measure of spread and the difference between population and sample standard deviation.
This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.