A phrase such as “four weeks” looks like a simple duration. In a German employment contract it is only one part of the calculation. You also need to know when the notice is received and which termination dates the clause permits.
Start with receipt, not posting
A resignation normally becomes effective when it reaches the employer, not when you put it in the post. That makes the delivery day a planning fact. A letter left too late for the authorised recipient may shift the calculation, even if its date line shows the earlier day.
Read the whole clause
“Four weeks to the fifteenth or end of a calendar month” creates different possible endpoints from “one month to month-end.” Do not convert those phrases into the same number of days. Check whether probation wording, a collective agreement, or a later amendment changes the clause.
Build a small date table
Write down three columns: latest safe receipt date, resulting contractual end date, and evidence of delivery. Then add practical dates—manager conversation, planned leave, return of equipment, and next-role start—without confusing them with the legal employment end.
If the wording is inconsistent or the outcome affects an accepted offer, get qualified legal advice before relying on your own calculation. A planning consultation can help identify exactly what remains uncertain.