when does vs when will to ask the future event

Question

I want to ask when school will start.

I feel both of the following expressions are acceptable.

When does his school start?

When will his school start?

The school will start at the future time so the use of 'will' seems natural. But I feel the sentence with 'does' is fine also. I don't know why it's correct though.

What expression is more idiomatic?

Answer 1

We can, and often do, use the present tense for future events that are, in the present, scheduled, planned, or expected, e.g.:

When does your train leave?
My vacation starts on the 3rd of September.
The meeting is at 2PM tomorrow.

The Present Simple Tense - Future Plans & Scheduled Events