When is it?

"When is it?" is a normal way to ask when something is going to happen.

A: Do you think you can make it out to my art show?

B: Um, when is it?

A: It's next Saturday, in the afternoon.

If someone told you when something was going to happen, but you forgot, you could also ask:

When was it?

You can ask this way, even if the event hasn't happened yet.

This phrase appears in these lessons: