am going/will go

[Unregistered]

I wonder if there is any difference between (1) and (2).
If so, which is natual, (3) or (4)?

1. I'll go to bed.
2. I'm going to bed.

3. I'm tired, I'll go to bed early tonight.
4. I'm tired, I'm going to bed early tonight.

Have a nice day!

[RonBee]

I wonder if there is any difference between (1) and (2).
If so, which is natual, (3) or (4)?

1. I'll go to bed.
2. I'm going to bed.

3. I'm tired, I'll go to bed early tonight.
4. I'm tired, I'm going to bed early tonight.

In sentence 1 the speaker is stating his intentions. Sentence 2 is more certain. (The "going" is probably going to happen right away.) Sentence 4 is more likely than sentence 3.