You can use the present perfect progressive: "How long have you been studying English?" The activity started in the past and continues (progresses) into the present. You could also use "How long have you studied English?" without a difference in meaning. You don't need the preposition "for" in these questions, but you will probably hear "for" or "since" in the answer.

Hi Augusto, By using the present continual ("are you studying") and asking how long, you're suggesting that the other person will completely stop learning English in the near future. If they already know English and are continuing their study, perhaps your question should be, "For how long have you been studying English?" This acknowledges that they started study well before you asked this question.

Augusto, *They are both correct. Although in the first sentence the "for" should be placed at the beginning in formal speech or writing. In everyday conversation people often place a preposition at the end of a question. examples -For how long are you studying English?.......How long are you studying English for? -To whom are you talking....... Who are you talking to? -For whom are you looking ?....Who are you looking for? *If someone is studying now and you want to know for how much longer, you can use the present continuous to express the future. -For how long are you studying English?....meaning the person is studying now and you want to know for how much longer they are planning to study. -For how long are you going to study English....meaning...what is the person's intention... In this case there is no practical difference between "going to study" and "are studying" (between a plan and an intention). -For how long will you be studying English....means in the future or from this point on, how long will you be studying? At the library a friend approaches and says, "A few of us are going to the bar, would you like to come along? -I would like to but I can't. I'm studying English for the exam tomorrow. -How long are you studying for? ( How long are you planning to study?) -For at least another hour. -Stop by afterwards. I'm sure we will still be there. -Ok, I'll do that.

How long have you been studying English?

Neither is correct. Here are a couple: How long have you been studying for? How long will you be studying for? How long are you going to study for? How long did you study for? **You cannot say: How long are you studying for**