Date Difference Calculator
Find the exact number of days, weeks, months, and years between two dates.
Finding the exact gap between two dates comes up more often than it seems — how many days until a deadline, how long a project has been running, or how many weeks are left before an event. Counting on a calendar by hand is error-prone, especially across month boundaries with different day counts.
This calculator handles that arithmetic precisely, showing the difference broken down as years, months, and days, alongside the total number of days, weeks, and months for whichever unit is most useful for the situation.
An optional toggle lets the end date itself be included in the count — useful for questions like 'how many days is a 3-day event that starts on the 1st and ends on the 3rd' where the answer depends on whether both endpoints are counted.
Step-by-step instructions
- 1
Enter the start date
Pick the earlier date, or whichever date you're counting from.
- 2
Enter the end date
Pick the date you're counting to.
- 3
Toggle 'include end date' if needed
Turn this on if the end date itself should count as a day (common for counting inclusive date ranges like event durations).
- 4
Read the results
See the exact years/months/days breakdown, plus total days, weeks, and months.
Common use cases
Counting down to a deadline or event
Find exactly how many days remain until a specific date.
Measuring how long something has been running
Calculate the exact duration between a start date and today or another end date.
Calculating an inclusive date range
Use the include-end-date toggle to correctly count multi-day events or booking durations.
Contract or lease term calculations
Find the exact length of a period defined by a start and end date.
Tips for best results
- If you're counting a booking or event duration where both the start and end day should count, turn on 'Include the end date' — otherwise the last day is excluded from the total.
- The years/months/days breakdown accounts for actual calendar month lengths, so it's more precise than dividing total days by 30.
- If the end date is entered before the start date, the tool still calculates correctly by using the absolute difference.
Frequently asked questions
Should I include the end date or not?
It depends on what you're counting. For 'how many days until X', leave it off. For counting the total days in a range that includes both endpoints (like a 3-day conference from the 1st to the 3rd), turn it on.
Is my data stored anywhere?
No — the calculation happens entirely in your browser using JavaScript. Nothing is sent to a server or saved.
What if I enter the end date before the start date?
The calculator automatically handles this and shows the absolute difference between the two dates, with a note that they were reordered.
Why doesn't total months equal total days divided by 30?
Months vary in length (28-31 days), so the tool calculates actual calendar months rather than using a flat 30-day approximation, which is more accurate.