The temporal preposition ‘für’ is used when indicating duration (e.g. for a week).
‘Vor’ is used to indicate an event or activity that started and ended at some point in the past (English equivalent of adding “ago” to a time expression; e.g. four weeks ago / vor vier Wochen).
The temporal preposition ‘seit’ is used to indicate something that began in the past and continues into the present, as can be seen in this translation of the third example under “Seit wann?” above:
Ich fahre seit einem Jahr Auto. / I have been driving since last year.
Literally translated, “seit“ in German means since, but it is used other ways, too. In English, “since” is used to mark the beginning of a period of time (I have been here since 2015), whereas in German, “seit” can also be used similar to the way English speakers use “for,” and “vor” is used similar to the way English speakers use “ago.”
Vor 5 Jahren = 5 years ago
Seit 5 Jahren = For 5 years
Seit 2015 = Since 2015
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ab – refers to a starting point in time (e.g. ab 10.00 Uhr / starting at 10:00)
bei – used when discussing an activity that one is doing (e.g. bei der Arbeit / while working/during work)
bis – ‘until’ (e.g. Ich muss bis 17.00 Uhr arbeiten. / I have to work until 5:00 pm.)
in – used in conjunction with a future time (e.g. in einer Stunde / in an hour)
nach – ‘after’ (e.g. nach der Pause / after the break)
seit – ‘for’; used when expressing something that happened in the past but continues on into the present (e.g. seit einer Woche / for a week; Ich lebe seit einem Jahr in Bonn. / I have been living for a year in Bonn.)
vor – ‘before’ or ‘ago’ (e.g. vor den Ferien / before the vacation/holidays; vor zwei Tagen / two days ago)
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These temporal prepositions take the dative case, except ‘ab’ and ‘bis’ (the latter refer to particular times), which take the accusative (e.g. bis nächste Woche; ab den zehnten Juni). Further, the following questions are associated with these prepositions:
Ab wann? → ab → ab Samstag
Bis wann? → bis → bis 15 Uhr
Seit wann? → seit → seit zwanzig Jahren
Wann? → in → in einem Monat
Wie lange?* → bis → bis nächsten Dienstag
*’Wie lange?’ can also be answered without using a preposition (e.g. Wie lange dauert es? Zwei Stunden.).
