Time span prepositions (von... bis, seit, für)

From... To...

To express the beginning and end of a time span, use von (from) and bis (until / to). You will often use this with the days of the week, which do not require an article here.

The verb dauern (to last) is very useful for describing these durations.

Since and For (Ongoing Actions)

To talk about something that started in the past and is still happening now, German uses the preposition seit.

Depending on whether you are talking about a specific starting point or a duration of time, seit translates to either "since" or "for". Because the action is still ongoing, German uses the present tense, unlike English which shifts to the present perfect ("have been").

seit always requires the dative case. For masculine nouns like der Tag (the day), the indefinite article ein becomes einem.

For (Planned Durations)

When you want to say "for" to talk about a planned appointment, a deadline, or an intended future duration, use the preposition für.

Unlike seit, für always requires the accusative case.

Here is a quick comparison of how the masculine noun der Tag changes depending on whether you are looking back at an ongoing duration (seit) or looking forward to a planned duration (für):