SIMPLE FUTURE:
The simple future (will + infinitive) is used to indicate:
1.- A future prediction:
I'm sure you will have a wonderful time tomorrow.
2.- A spontaneous decision:
I'm hungry. I'll have a sandwich.
3.- To make an offer, a promise or a threat.
I promise I will pass this test.
4.- Future actions happening without the speaker's intention (birthday, weather, etc.).
I will be 18 tomorrow.