Future Tense — will / be going to

There are two expressions for talking about the future: will and be going to. Their meanings are similar, but their nuances are slightly different, so it is important to use them appropriately.

Basic Rules

will + base form of the verb expresses “will probably ~” (a prediction) or “intend to ~” (a decision made at the moment). Will is natural for something decided right now while speaking or for a prediction.
be going to + base form of the verb expresses “intend to ~” (a plan decided earlier) or “be likely to ~” (a prediction based on signs). Be going to is suitable for something planned in advance or a prediction supported by signs in front of you.
The negative forms are will not (won't) / be not going to, and the question word orders are Will + subject ~? / Be + subject + going to ~?

Points to Note

① Short forms of will: I'll, you'll, he'll, she'll, we'll, they'll. The negative is won't (will not).
② The meaning can change with will / be going to: “The phone is ringing!” “I'll get it.” ← This is a decision made at the moment, so will is used. “I have a plan. I'm going to study abroad next year.” ← This was decided in advance, so be going to is used.
③ Use the present tense for future events inside when / if clauses of time or condition: “I will call you when I arrive.” × when I will arrive. This is an important junior high school English rule.
④ At the junior high school level, shall is often used in suggestions such as “Shall we ~?” and “Shall I ~?”

Practice

1. Write “I am going to go to London next week” using be going to.
2. Write “It will be sunny tomorrow” using will.
3. Correct the error: If it will be sunny tomorrow, we will go to the beach.