When to Use Wann and Wenn in German

English "when" can be expressed in German by three different words: als, wann, and wenn. In the past tense, "when" is usually als: "Als er gestern ankam," or "When he arrived yesterday." But here we will concentrate on the two German "w" words for "when."

'Wann' Is Related to Time

In general, wann is a question word related to time, even when used in a statement. It usually asks or relates to the question "when?" In a statement such as "I don't know when the train is arriving," the word wann would be used. (See examples above.) It can sometimes mean "whenever," as in "Sie können kommen, wann (immer) sie wollen."

• Wann kommt dein Bruder? | When is your brother coming?​
• Ich weiß nicht, wann der Zug ankommt. | I don't know when the train is arriving.
• Sie können kommen, wann (immer) sie wollen. | They can come whenever they want.
• Seit wann wohnst du in Berlin? | How long (since when) have you been living in Berlin? 

Four Situations That Call for 'Wenn'

The word wenn (if, when) is used more often than wann in German. It has four main uses:

1. It can be subordinating conjunction used in conditionals ("Wenn es regnet," or "If it rains").
2. It can be temporal ("jedes Mal, wenn ich," or "whenever I"), usually translating as "whenever" in English.
3. It can indicate concession/conceding ("wenn auch," "even though").
4. It is used in wish-phrases with the subjunctive ("wenn ich nur wüsste," "if I had only known").

• Wenn er nervös ist, macht er Fehler. | When he's nervous, he makes mistakes.
• Immer, wenn er nach Hause kommt, ist es sehr spät. |Whenever he comes home, it's very late.
• Wenn ich nur gewusst hätte! | If I had only known!
• Wenn man da oben steht, kann man sehr weit sehen. | When you stand up there, you can see very far.