
dran sein
to be up
Colloquial for being one's turn to do something.
Ich habe die letzte Runde bezahlt, jetzt bist du dran.
I paid for the last round; now you're up.
on it / attached
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to be up
Colloquial for being one's turn to do something.
Ich habe die letzte Runde bezahlt, jetzt bist du dran.
I paid for the last round; now you're up.

to be attached
Colloquial for 'to be fastened' or 'to be stuck on'.
Pass auf, der Zettel ist nicht mehr richtig dran und könnte abfallen.
Careful, the note isn't properly attached anymore and could fall off.

to be on it
Colloquial for currently working on a task or pursuing a matter.
Ich bin dran an dem Problem, ich melde mich, wenn ich eine Lösung habe.
I'm on the problem; I'll get back to you when I have a solution.

to be on the line
Colloquial for currently speaking on the phone or being on the line.
Kannst du kurz warten? Meine Mutter ist noch am Telefon dran.
Can you wait a moment? My mother is still on the phone.
'Dran' is the colloquial short form of the adverb 'daran' (on it / at it). It is used very frequently in spoken language instead of 'daran', especially in fixed expressions with 'sein' (to be).
Denk dran, die Blumen zu gießen!
Remember to water the flowers!
The word 'dran' clearly belongs to colloquial language. In formal or written texts, you should use the full form instead or a suitable paraphrase.
Wer ist als Nächstes dran mit dem Vortrag?
Who's up next with the presentation?
The most common meaning of 'dran sein' is that it is one's turn. This can refer to games, tasks, or a queue.
Du hast gewürfelt, jetzt bin ich dran.
You rolled the dice; now I'm up.
The phrase 'an etwas dran sein' means that you are currently working on something or pursuing a problem. The preposition 'an' followed by the dative makes this meaning clear.
Ich bin an einer Lösung für das IT-Problem dran.
I'm working on a solution to the IT problem.
there / since / then
On the phone, da and dran can both ask whether the other person is still present or reachable. Da focuses on presence and the ability to respond. Dran emphasizes that the phone connection is still active. Use dran when being on the line is what you mean.

Bist du noch dran, oder ist die Verbindung abgebrochen?
Are you still on the line, or did we get disconnected?
Bist du noch da, oder ist die Verbindung abgebrochen?
Are you still there, or did we get disconnected?