Date Difference Calculator
Find the exact number of days, weeks, months, years, and business days between any two dates.
About the Date Difference Calculator
This tool calculates the difference between two calendar dates and returns the result in several useful units. Enter a start date and end date, then click Calculate to see the total days, complete weeks, approximate months and years, and the number of weekday (Monday–Friday) business days.
All calculations run in your browser using JavaScript's built-in Date object — no data is sent to a server. The calculator handles dates across month, year, and century boundaries.
Frequently Asked Questions
How is the difference calculated?
The total number of days is calculated from the exact millisecond difference between the two dates divided by 86,400,000 (milliseconds per day), then rounded to the nearest whole day. Weeks are the floor of days ÷ 7. Months and years are approximate calendar-based calculations.
What counts as a business day?
Business days are Monday through Friday, excluding weekends. The calculator does not account for public holidays, which vary by country and year.
Why do months and years show "approx."?
Calendar months have different lengths (28–31 days) and years can be leap years, so the number of complete months or years between two dates depends on which specific months are involved. The values shown are the nearest whole calendar months and years.
What if I enter the end date before the start date?
The calculator automatically swaps the dates so the result is always positive. A note (*) is shown on the day count to indicate the dates were swapped.
Can I calculate differences across centuries?
Yes. JavaScript's Date object handles any valid Gregorian calendar date.