Will and Going To

We use Will and Going to when we want to refer the future, but sometimas could be very confusing to know which one to use.

There is a slight difference between the two but in the most causes can be used with no differences in meaning. Even a native speake is going to understand you without problems

Will vs Going to: Uses

Will  

- Fast Decisions (For thinks we decide to do right now)                                                       

Example: I will buy a car      

- Offers

Example: I will help you with that.

- Threat

Example: If you don't study, I will tell your mother.

- Refusal (When we refuse to do something we use Won't)

Example: I won't go to the concert tomorrow.

- Promise

Example: Don't worry, I will keep the secret

Going to

- Plan

Example: When you are planing something or decision was made before the moment of speaking: Im going to travel to Concepcion next weekend.

- Signs

Example: When there are signs of something is going to happen.

I feel dizzy, i think i'm going to vomit.

Actually we can use Will and Going to make predictions.

We use will for predictions when we have no real evidence: It will rain tomorrow! (It's a feeling but i can't be sure)

We use going to for predictions when we have some real evidence: It's going to rain tomorrow! (You see a big, black cloud in the sky so if it doesn't rain i'll be very surprised)

I think it will tonight.

I think it's going to rain tonight.

Its 8:30!, I think i'm going to miss the train

Its to late!, I think i will miss the train