Just to add some extra confusion: the future tense can also be used in Italian for speculating on facts (I am not sure the same occurs in English, though).
So for instance imagine the following conversation:
A: "Perché Mario non è venuto a scuola oggi?"
B:"Non so, SARÀ malato".
A is wondering why Mario did not show up at school, and B is GUESSING Mario is sick; therefore it is much like saying "I guess he is sick". That being said, when the future tense conveys this nuance of guessing, speculating on facts, it really can be used in the progressive tense, for example:
A:"Dov'è il professor Rossi? Non lo trovo da nessuna parte"
B:"STARÀ FACENDO lezione in qualche classe"
The translation is as follows:
A:"Where is sir Rossi? I can't find him anywhere"
B:"I GUESS he IS HAVING a lesson in one of his classrooms".
Hope this helps.