Count days or shift a date
This calculator does both: it counts the days between two dates — as days, weeks plus days and an exact years/months/days breakdown — and in “date plus/minus” mode it shifts a start date by a number of days, weeks, months, years or working days, forwards or backwards. Everything runs locally in your browser.
How does the difference between two dates count?
Pick two dates and you instantly see the difference. By default the end date is not counted (June 1 → June 10 = 9 days); one checkbox includes it. Swapped dates are reversed automatically, so the difference is always positive.
Counting nights vs. counting days
The default counts the distance between the dates — like nights in a hotel or the answer to “how many days until…”. Including the end date counts both endpoints, which fits rental periods, medication courses or attendance: Monday through Friday is then 5 days instead of 4. Getting this distinction wrong is the most common off-by-one error in date maths.
How the breakdown works
The years/months/days breakdown anchors at the start date and counts full calendar months first, clamping month ends (January 31 + 1 month = February 28/29) — the same convention used for deadlines and ages. Because months differ in length (28–31 days), “3 months” is not a fixed number of days: across a year it averages about 30.44 days per month.
What is January 31 plus one month?
February 28 — or February 29 in a leap year — and never March 3. The “date plus/minus” mode counts whole calendar months from the start date and clamps the day to the length of the target month; this is exactly how deadlines and ages are reckoned. The same rule turns February 29 plus one year into February 28. The clamping is deliberately not reversible: from January 31, one month forward and back again lands on January 28 — convention, not a bug. Whenever clamping happened, the calculator says so below the result.
How are working days added?
With the “working days” unit the calculator skips Saturdays and Sundays, optionally also the nine nationwide German public holidays — and, with a federal state selected, that state’s additional holidays; the movable ones are derived from the Easter date using Gauss’s Easter formula. The start day itself is not counted: “10 working days from today” is the tenth working day after today, the same convention the spreadsheet function WORKDAY uses. One limit stays out on purpose: the rule of section 193 of the German Civil Code (BGB), which moves a deadline falling on a Saturday, Sunday or public holiday to the next working day, is not applied — legally binding deadlines belong with a professional.
Typical uses
Payment terms (“due in 30 days”), delivery dates (“10 working days from today”), project durations, notice periods, visa stays, pregnancy weeks, subscription periods, days until an event or between invoices — anywhere “how long is it exactly?” or “which date is that?” needs a precise, reproducible answer rather than a guess.
Private by default
All dates and numbers are processed entirely on your device — no upload, nothing leaves the browser; only the calculator’s settings are remembered locally by your browser. The calculator works offline too.