"you know what?" or how to change your mind

Question

What are some ways in which one can express "you know what?" expressions with a nuance of either "i've made up my mind" after debating something internally for awhile? I see that やっぱり or 実は are somewhat close but doesn't quite fit.

For example

A: "You going to the meet up tomorrow?"

B: "I'm not sure..."

A: "Well let me know before Friday"

B: "You know what? I'll go."

Answer 1

So you mean "you know what" used in this scene? https://youtu.be/rk_qLtk0m2c?t=2m58s

It's difficult to give a direct equivalent, but possible expressions would be:

• こうしましょう！　こうしよう！
  _{(This こう refers to something that follows.)}
• それじゃあ！　それでは！
• では！　じゃあ！
• 決めた！　決めました！　わかった！　わかりました！
• よし！　オーケー！

Answer 2

This is one of those situations where, in my opinion, there are several different ways of expressing this idea.

Here's how I would translate your example:

A: 明日｛あした｝、会｛あ｝うつもりですか？
B: 分｛わ｝からないんですけど。
A: なるほど、土曜日｛どようび｝の前｛まえ｝に行｛い｝くか、行｛い｝かないかを知｛し｝らせて下さい。
B: あのね、少｛すこ｝し考｛かんが｝えたら、会｛あ｝うつもりです。

As I'm sure you're aware, the phrase "You know what?" is an English expression that the Japanese would find funny if you translated it directly. In my experience, if you say something to the effect of "now that I think about it..." you'll be able to communicate the idea that you have just made your made a decision. Just know that in the situation above, person B will probably have to reaffirm that they can meet up if the relationship between A and B is formal.

Another way to do it is to just say "I've made my decision."　Translation using this structure below:

A: 明日｛あした｝、会｛あ｝うつもりですか？
B: 分｛わ｝からないんですけど。
A: なるほど、土曜日｛どようび｝の前｛まえ｝に行｛い｝くか、行｛い｝かないかを知｛し｝らせて下さい。
B: 決｛き｝めた、会｛あ｝うつもりです。

In reality, a lot of this depends on the relationship between A and B, as well as the environment where the conversation happens.