Present Tenses for Future :
I’m doing something (tomorrow etc.) = I have already decided and arranged to do it:
a: What are you doing on Sunday morning ? (not What do you do)
b: I’m going for a walk . (not I go)
We do not normally use will to talk about what we have arranged to do:
What are you doing tonight? (not What will you do)
I’m visiting my parents tonight. (not will visit)
We also use the present continuous for an action just before you start to do it. This happens especially with verbs of movement (go/come/leave etc.):
I’m tired. I’m going to bed now. (not I go to bed now) ‘
Steve, are you ready yet?’ ‘Yes, I’m coming.’ (not I come)
Present simple (I do) with a future meaning
We use the present simple when we talk about timetables and programs (for example, transport or cinema times):
I have to go. My train leaves at 10 o’clock.
What time does the film start tonight?
You can use the present simple to talk about people if their plans are fixed like a timetable:
I start my new course on Monday.
What time do you finish work on Friday ?
But the continuous is more usual for other personal arrangements:
What time are you meeting Kate tomorrow? (not do you meet)