When to use will and going to for future intentions is often confusing for non-native English speakers.

Both will and going to are used to express a future action that we have a strong intention of doing. So, what’s the difference? It’s all about when the decision is made. Let’s look.

• We use will when we we make a spontaneous decision to do something.
• We use going to when the decision to do the action was made before the time of speaking.

example: “Hey John, I am going to have a party on Friday,” said July. “Really, I will bring the music,” John replies.

July uses going to because her decision to have the party was made before the time of speaking.

In this case, John had no idea about the party before July told him. Therefore, he uses will to spontaneously respond and tell her that he will bring the music.

So, we use will when we make a spontaneous decision about something that we intend to do in the future, and going to when we are talking about a predetermined plan.

I hope that helps. Let me know what you think in the comments.