Date Difference Calculator

About the Date Difference Calculator

This works out exactly how much time lies between two dates — as a calendar breakdown (years, months and days) and as totals (days, weeks, months). It's handy for counting down to or back from an event, working out the length of a project or contract, checking notice periods, or answering "how many days have passed since…". Pick a start and end date and it does the rest, correctly accounting for month lengths and leap years.

How it works

The total days is the exact number of days between the two dates. The calendar breakdown (years, months, days) is computed the way you'd do it by hand — subtracting each part and borrowing across month and year boundaries, using each month's real length. Weeks and days and total months are derived from those. An option lets you include the end day in the count (so a Monday-to-Friday span can read as 4 days or 5, depending on whether both ends count).

Assumptions and behaviour

• The start date must be on or before the end date, or it prompts you to fix it.
• Leap years and varying month lengths are handled automatically.
• By default the count is the plain difference (end minus start); tick include the end day to count both endpoints.
• It works with whole calendar dates — no time of day or time zones.

Limitations

• Total days and total months describe the same span differently and won't reconcile by simple division, because months vary in length — both are correct measures.
• It counts calendar days, including weekends and holidays; for business days only, use the Work Days Calculator.
• There's no time-of-day component, so it isn't suited to precise hour/minute durations (use the Time Duration Calculator for that).
• Very distant historical dates rely on the browser's calendar, which uses the modern (proleptic Gregorian) calendar.

Privacy

The calculation runs entirely in your browser. Your dates are never uploaded or stored.