Will or going to?

Talking about future actions

We use both will and going to to talk about our future actions, but there is a clear difference. Study this example situation.

Helen's bicycle has a flat tire. She tells her father.
Helen: My bicycle has a flat tire. 
           Can you fix it for me?
Father: Okay, But I can't do it now.
            I'll fix it tomorrow

Note: We use will when we decided to do something at the time of speaking. The speaker has not decided before. before Helen told her father, he didn't know about the flat tire.

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Later, Helen's mother speaks to her husband.

Mother: Can you fix Helen's bicycle?

             It has a flat tire.

Father: Yes, I know. She told me.

            I'm going to fix it tomorrow.

Note: We use going to when we have already decided to do something. Helen's father had already decided to fix the bicycle before his wife spoke to him.

Here is another example.

• Tom is cooking when he suddenly discovers that there isn't any salt.
• Tom: Ann, we don't have any salt.
• Ann: Oh, we don't? I'll get some from the store. (she decides at the time of speaking)

Before going out, Ann says to Jim.

• Ann: I'm going to get some salt from the store. (she has already decided)
•         Can I get you anything, Jim?

Saying what will happen (predicting future happenings)

We use both will and going to to say what we think will happen in the future.

• Do you think Laura will get the job?
• Oh no! It's already 4:00. we're going to be late.

We use going to (not will) when there is something in the present situation that shows what will happen in the future (especially the near future). The speaker feel sure about what will happen because of the situation now.

• Look at those black clouds. It's going to rain. (the clouds are there now)
• I feel terrible. I think I'm going to be sick. (I feel terrible now)

Do not use will in situation like these.

In other situations, use will

• Sue will probably arrive at about 8 o'clock.
• I think George will like the present you bought for him.