Somebody requested that I teach a lesson on the differences between

“will” and “going to.”

“Will” and “going to” can both be used when making predictions.

These next two examples mean the same thing:
- I think I will be too tired to go to the movies tonight.
- I think I’m going to be too tired to go to the movies tonight.


Here are some differences:

“Will” is used with rapid decisions, offers, promises, threats, and refusals.

Examples:
Rapid decisions: I’m tired, so I think I will take a nap.

Offers: I will help you with your homework if you want me to.

Promises: I will not tell anyone the secret that you told me.

Threats: If you leave the house, I will tell your father.

Refusal: She will not eat meat because she is vegetarian.


“Going to” is used with prior plans. It can also be used when there is evidence that something is going to happen.

Examples:
Prior plans: I’m going to go shopping with my mom tonight.
(The speaker made plans to go shopping with their mom before speaking.)
- She is going to a concert this weekend.
(The speaker already had plans to go to a concert before saying it.)

When there is evidence that something is going to happen:
- There are a lot of clouds in the sky, so I think it is going to rain.
(The fact that there are clouds is a sign that it might rain.)
- The score of the baseball game is 3-2. I think my favorite team is going to win the game.