will vs be going to

This is a grammar point that frustrates a lot of students. When should I use "will" and when should I use "be going to?" It's not an easy question to answer. This is partly because there are a lot of instances where either is correct. For example, in the case of a general prediction (a guess about the future), either will work. Consider:

• "The King's Speech" is going to win the Oscar for Best Picture.
• "The King's Speech" will win the Oscar for Best Picture..

Both are correct. Both are predictions about a future event. Both are general. However, when there is something in the present that leads to the prediction, then use "going to."

•  Look at the clouds. It's going to rain.  

"Be going to" is also used in the case of a plan for the future.

• We are going to a movie on Friday.
• We are going to go to the mall after that. 

"Will" on the other hand is used for an offer or when someone volunteers for something. It is also used for making (or refusing) a request or for making a promise. (The first two are examples of requests, the third sentence is an example of volunteering or offering to do something.)

• Will you stop at the store on your way home and buy some milk?
• I asked Jim to buy the milk, but he won't do it.
• A: Oh the telephone is ringing. B: I'll get it. 
• I will love you forever.  
• If it takes forever, I will wait for you.

 "Will"is also used to talk about general truths. 

•  The sun will come up tomorrow.
• Water will freeze at 0 degrees Centigrade. 

"Will" is also used when the decision is made at that moment.This is different from using "be going to" for plans because it is not a plan made in the past, but that is sudden. 

• A: There is a lecture tonight by Bill Gates. B: Oh wow! That's cool. I think I'll go!

Okay,  here are some sites for practice.Here is an eight question multiple choice exercise. A good way to get started. Next, look here for more explanation and then do exercises 18, 19, and 20. This site doesn't have any explanation, but it does have a short simple fill-in-the-blank exercise. Here is another fill-in-the-blank exercise. You need to complete the sentence with the verb in parentheses and either "will" or "be going to." Here is another quick exercise. Like the last one, you will need to complete the sentence with "will" or "be going to" plus the verb in parentheses. This exercise will take a little more work. You need to use the correct form of the future (will or be going to) AND put all the words in the correct order.