If I cast Expeditious Retreat, can I Dash as a bonus action on the same turn?

Question

I am new to D&D, and am playing 5th Edition. I have a level 3 wizard who has the spell expeditious retreat:

This spell allows you to move at an incredible pace. When you cast this spell, and then as a bonus action on each of your turns until the spell ends, you can take the Dash action.

The scenario is: On my character's turn, I want to Disengage from an enemy within 5 feet of me so as to not provoke an opportunity attack. I move my character 30 feet away. I then cast the spell expeditious retreat (which has a casting time of 1 bonus action) and then move another 60 feet.

The problem is that my DM says that I cannot take the Dash action, because he says that my bonus action is the casting of the spell. I believe that I can take the Dash action, because the spell says when you cast this spell you can take the Dash action.

Which one of us is correct?

Answer 1

You are correct (mostly).

The description for Expeditious Retreat reads as follows (emphasis added)

This spell allows you to move at an incredible pace. When you cast this spell, and then as a bonus action on each of your turns until the spell ends, you can take the Dash action.

The intention for the spell is that casting it allows you to make a fast getaway. It'd be a lot less useful if it only worked on the turn after casting. It's worth noting that the Dash action allows you to make an additional move, so the total you can move in a round with a speed of 30ft, having used an action to Disengage and then a Bonus Action to Dash is 30ft (movement) +30ft (Dash) = 60ft, not 90ft as "and then-for another 60ft" in your question seems to imply.

As goodguy5 points out in a comment on this answer, if you devoted your entire turn to Move (30ft), Dash as an Action (+30ft), and cast Expeditious Retreat as a Bonus Action (+30ft), you could move 90ft in a round. This would, of course, provoke an Opportunity Attack, though.

Hope that helps!