未來簡單式的動詞有兩種形式

1. will + 原形動詞

2. be going to +原形動詞

都是表達未來的動作或狀態，但使用上可能會有些微意義上的差異。

1. 常見的差異

例如

1. Mary is going to throw a party at her apartment this weekend.  (說話前早已決定並計畫好的事情)

2. I'm going to visit my niece in Tokyo this summer. (說話前早已決定並計畫好的事情)

3. A: What do you want to do this weekend? B: I don't know yet. Maybe I'll visit my grandma. (說話當下做出的決定)

4. She's going to buy a new car next week. (說話前已決定，較近期的未來計畫)

5. When I grow up, I will buy myself a nice sports car. (較遠期的未來計畫)

6. I believe Jane will like the dress you choose for her. (個人意見與推測，不確定性高)

7. The house is too old. It will not survive the next earthquake. (個人意見與推測，不確定性高)

8. You need to be careful when handling broken glass, or you will cut yourself. (個人意見與推測，不確定性高)

9. Put that down! You are going to hurt yourself! (根據可見證據預測，發生機率高)

10. Bring an umbrella with you. It's going to rain. (根據可見證據預測，發生機率高)

2. 此外承諾別人願意幫忙的事情，或是單純描述未來的事實，則會較常使用will

例如

1. I will take you out for dinner if you finish your homework by 5 p.m.

2. Tomorrow will be another day.

3. 條件句型中，副詞子句中的未來動作要使用現在簡單式，主要子句則使用「will+原形動詞」或「現在式的助動詞+原形動詞」。

例如

1. If you leave now, you'll get there in time.

2. If you speak to the manager, I'm sure he'll help you.

3. When Simon visits us this summer, we will take him to our favorite restaurant.

相關文法，請參考「第一條件句」

4. 未來確定的計畫可用現在進行式代替未來式

例如

1. I'm leaving tomorrow. I've got my ticket.

2. I'm going out tonight. I have a date.

5. 既定好的行程或公務類的行程，用現在簡單式即可。

例如

1. The train leaves at 10:00.

1. 使用will+原形動詞的句型，以will作為該句的主要動詞進行肯定否定和疑問句的變化。

2. 使用be going to +原形動詞的句型，需搭配主詞人稱使用適當的be動詞，並以該be動詞進行肯定否定與疑問句的變化。

1. 使用正確未來式動詞形式
   例句
   She’s going visit her friend in Hong Kong.(X)-少了to
   She's going to visits her friend in Hong Kong.(X)-visit不用加s
   She will visits her friend in Hong Kong.(X)-visit不用加s
   She’s going to visit her friend in Hong Kong.(O)

2. will 還是 be going to?
   例句

Don’t worry! I’m going to help you.(X)
Don’t worry! I’ll help you.(O)
[說話當下的決定，要使用will]

If I find your pen, I’m going to send it to you.(X)
If I find your pen, I’ll send it to you.(O)
[條件句型中的主要子句未來動作要使用will]

Be careful! You will spill your coffee.(X)
Be careful! You’re going to spill your coffee.(O)
[目前已可見的證據預測，發生機率高用be going to]

I’m not going to be home tomorrow when the painters come to paint my apartment.(X)
I won’t be home tomorrow when the painters come to paint my apartment.(O)
[條件句型中的主要子句未來動作要使用will]