I'll get back to you

We use this expression to say that we need to find some information or do something and will contact the person later.

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Written	Yes
Spoken	Yes
Formal	No
Informal	Yes

Example 1

Can you tell me how many students are taking the exam next month?
I'll find out. I'll get back to you.

Example 2

Do you know what has been decided?
Not yet. I'll get back to you on that.