Datumsrechner +/− Tage

How the +/- date calculator guarantees accuracy

This calculator adds or subtracts days with UTC math to avoid daylight-saving jumps. Days and weeks shift by simple integer steps; business-day mode walks day by day and skips Saturdays and Sundays, so a Freitag plus 1 Werktag landet immer auf Montag. Months and years use clamped month arithmetic: when you add one month to 31 January, it lands on 28 (or 29) February because the day is clamped to the last valid date. The logic never uses browser locale time zones, so results stay stable across devices.

Start by picking a date, choose whether you want to go forward or backward, then set amount and unit. Toggle Werktage to exclude weekends. The summary shows ISO dates, weekday labels, and both calendar and business-day deltas. Because calculations are inclusive-exclusive (start day is not counted, each step moves one day), you avoid off-by-one errors for project timelines, delivery windows, SLA clocks or legal response periods. Everything runs locally in your browser; no API calls or data storage.

Best practice: use calendar days for general schedules and business days for service tickets, banking, and office workflows. For end-of-month billing, keep month-add clamping in mind: adding one month to any date picks the last valid day when the target month is shorter. For audits, export ISO strings and screenshot the summary so that your timeline is reproducible. If you need to include holidays, add them manually as non-working days in your own checklist; this tool excludes only weekends by design.

FAQ

• Warum UTC? UTC vermeidet DST-Verschiebungen, die bei Mitternachtsarithmetik Offsets erzeugen.
• Was ist inclusive-exclusive? Der Starttag zaehlt nicht, jeder Schritt verschiebt um einen Tag, damit Fristen konsistent bleiben.
• Werden Feiertage beruecksichtigt? Nein, nur Wochenenden werden entfernt; fuege Feiertage manuell hinzu.
• Wie behandelt ihr Monatsende? Der Tag wird auf das Monatsende geklemmt, damit 31. +1 Monat nicht ueberlaeuft.