I’m always shocked when students don’t know this one. What are you up to means what are you doing? It is probably the most common question someone will ask you after they haven't seen you for some time.
The answer is not GOOD❌ Because the question is not “How are you?” The question is what have you been up to: what have you been doing lately? What’s going on in your life recently? What’s new? They just want to hear about your life.
You can tell them anything: if you’ve been focused on work say something about work. Focused on family? Say something about family.
They probably don’t want an essay or a long drawn out answer. I know it can be hard to know how much to answer someone in English - this is actually hard for some native speakers too because it’s not always clear how much they want to know. A lot of it you have to infer from the situation.
Sample answers:
I’ve just been working a lot.
We just had a baby!
Studying and working.
It’s always safe to say one thing and turn the question around on the person who asked:
I’ve been working a lot…what about you?
