Can I calculate weeks or months between two dates?

Yes. The calculator shows the difference in days, weeks, months and years. Weeks = days divided by 7. Months use an average of 30.44 days.

What if the end date is before the start date?

The result will be negative. If you only care about the absolute gap, use the countdown calculator which shows the absolute value.

What calendar does the calculator use?

The Gregorian calendar, the international standard. For dates before the Gregorian adoption in your country, historical adjustments may be needed.

Date Difference Calculator — Days Between Two Dates

What is a date difference calculator?

A date difference calculator tells you exactly how many days, weeks, months and years lie between two calendar dates. It is useful for calculating age intervals, project durations, rental periods, warranty coverage, contract terms and the gap between any two events. The calculation runs entirely in your browser.

How the date difference is calculated

The calculator finds the difference by converting both dates to a common unit (milliseconds since the Unix epoch), subtracting, and then converting back to days. The basic formula is:

Days = (End date − Start date) ÷ 86,400,000

where 86,400,000 is the number of milliseconds in one day (24 hours × 60 minutes × 60 seconds × 1,000). Leap years are handled automatically because each date is converted to its absolute position on the timeline.

Step-by-step: find the difference between two dates

Select the start date. The earlier of the two dates you want to compare.
Select the end date. The later date. If you enter a date before the start, the result will be negative.
Click Calculate. You get the difference in days, weeks, months and years.

Common use cases

Rental period: Calculate how many days a tenant stayed to prorate rent or deposit refunds.
Warranty check: Find out if a product is still under warranty by comparing the purchase date to today.
Project timeline: Measure the duration of a project phase from kickoff to completion.
Age intervals: Calculate the exact age gap between two people or events.
Contract terms: Verify the length of a contract or lease period.
Pregnancy tracking: Count weeks from conception or last menstrual period.

Inclusive vs exclusive counting

There are two common conventions for counting days:

Exclusive (default here): End − Start. From Jan 1 to Jan 5 = 4 days. This is the standard for most calculations.
Inclusive: End − Start + 1. From Jan 1 to Jan 5 = 5 days (including both endpoints). Used for "how many days inclusive" questions.

If you need inclusive counting, simply add 1 day to the result shown.

Tips

Confirm the calendar. Our calculator uses the Gregorian calendar. Historical dates before the Gregorian adoption may need adjustment.
Time zones matter near midnight. Dates near midnight may shift depending on your time zone. For date-only calculations, this usually does not matter.
Months have varying lengths. When the result is shown in months, it is an approximation (30.44 days/month average). For precise month counts, count calendar months directly.

FAQ

Is the end date included?

No — we compute end − start, the standard convention. If you need both endpoints included, add 1 day to the result.

How are leap years handled?

Automatically. Each date is converted to an absolute timeline position, so Feb 29 is counted correctly.

Can I get weeks or months?

Yes. The result shows days, weeks, months and years. Weeks = days ÷ 7; months use a 30.44-day average.

What if the end date is before the start?

The result is negative. For the absolute gap, use the countdown calculator.

What calendar does it use?

The Gregorian calendar (international standard). Pre-Gregorian historical dates may need adjustment.