Date Difference Calculator

How the days are counted

The calculator counts from the start date up to the end date using real calendar dates, so month lengths and leap years are always right. Out of the box it gives the difference between the dates, which is how age, hotel stays and most deadlines are measured. From 1 January to 31 December 2026 is 364 days by this count: the gap between those two dates.

If you need to count every day in a range, including both ends, tick Include the end date. Then 1 January to 31 December 2026 becomes 365 days, the full calendar year.

When to include the end date

Whether to add the extra day depends on what you’re measuring:

• Leave it off for ages, durations, “how long ago”, hotel nights and time until a deadline.
• Include it for the number of calendar days an event covers, like a festival from the 3rd to the 5th (3 days), a holiday booked from Monday to Friday (5 days), or the days in a billing period that starts and ends on stated dates.

When a contract or form doesn’t say, it’s worth checking which one it means. The difference is always exactly one day.

Years, months and days between dates

Besides the total, the calculator breaks the gap into whole years, months and days, the same way an age is counted. For example, 1 January to 1 April 2026 is 3 months, even though it covers 90 days, because months have different lengths. When a date falls on the 31st and the target month is shorter, the month is complete on its last day, exactly as in our age calculator methodology.

Weekdays, weekends and working days

The Weekdays and weekends card counts Monday to Friday separately from Saturdays and Sundays across the range, and tells you which day of the week each date falls on. It’s a quick way to estimate working days for a project or notice period. Public holidays aren’t included, because they vary by country and region, so subtract the ones that apply to you.

Counting days by hand

For short spans, count the days left in the start month, add the full months in between, and add the days into the end month. Remembering month lengths is the hard part. The old rhyme helps: “Thirty days hath September, April, June and November”. All the rest have 31, except February with 28, or 29 in a leap year.

For long spans, add 365 for each full year plus one for every 29 February in between. In a spreadsheet you can simply subtract one date from the other; our guide to date and age formulas in Excel and Google Sheets shows how.

Related calculations

To count from a date of birth to today, the age in days calculator gives the same total along with milestones. To compare two birthdays, the age difference calculator shows who is older and by how much.

Last reviewed on 29 October 2026 by the Ageculator Team. See how we calculate.