Date calculator
Durations, deadlines and business days
Settings
Monday to Friday inclusive: 5 days instead of 4.
Result
About this tool
This calculator handles everyday date questions: how much time lies between two dates, what the deadline is 30 days or 10 business days from now, or which ISO week a given day falls in. Durations are shown in years, months and days, plus totals in days, weeks, hours and business days. Optional start and end times make the result more precise.
Business days run Monday through Friday and can exclude public holidays in mainland France, including Easter Monday, Ascension and Whit Monday, with an Alsace-Moselle option that adds Good Friday and December 26. Adding one month to January 31 gives the last day of February. The day info tab also shows the quarter, the day of the year and whether it is a leap year.
How to use it
- Pick a tab: “Duration between dates”, “Add or subtract” or “Day info”.
- For a duration, enter the “Start date” and “End date”, optionally the times, and check “Include the end day” if needed.
- For a deadline, set the “Start date”, choose “Add” or “Subtract”, then enter the “Amount” and pick the “Unit”.
- Check “Take French public holidays into account”, plus the Alsace-Moselle option if it applies, to adjust business day counts.
- Read the result on the right and copy the resulting date in ISO format with the “Copy” button.
Frequently asked questions
Which public holidays are supported?
The eleven public holidays of mainland France, with Easter Monday, Ascension and Whit Monday computed for each year. The Alsace-Moselle option adds Good Friday and December 26. Holidays from other countries are not included, and you can turn holidays off entirely.
What happens when I add a month to January 31?
If the day doesn’t exist in the target month, the calculator uses that month’s last day, so January 31 plus one month gives February 28 or 29 depending on the year. Adding years follows the same rule.
How is the ISO week number calculated?
It follows ISO 8601: weeks start on Monday and week 1 is the one containing the year’s first Thursday. As a result, the first days of January can belong to the last week of the previous year.
Are the dates I enter sent anywhere?
No. Every calculation runs in your browser with no network requests. Only the selected tab, the unit and the holiday options are saved locally in this browser for your next visit.