What have you been up to?

What are you up to? = What are you doing (now)? = O que você está fazendo?

Answer: (present continuous structure)

1. Not much. I'm just watching TV.

2. Not much. I'm just studying.

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What are you up to today? = What will you do today? = O que você vai fazer hoje/tem pra fazer hoje?

Answer: (future will/ to be going to/ gonna)

1. I'll just go to the doctor.

2. Not much. I'm just gonna hang out with some friends.

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What are you up to these days? = What have you been up to? = What have you been doing? = O que você tem feito esses dias?/como está sua vida?

Answer: (present perfect continuous structure)

1. Not much. I've just been working lately.

2. Not much. I've just been studying.