Better Ways to Say "I Don't Know"

Source: Speak Confident English


You should know the answer BUT you don't.

I'm not sure right now but I'll find out and get back to you soon.
I'll look into it and let you know what I find.
That's a really good question. I want to give you the most accurate answer that I can. I'll get back to you by the end of the day.

It's not your area of expertise, BUT someone wants to know what you think.

I'm not sure I'm the best person for you to ask, but here are my thoughts ...
Here's what I know and here's I don't know on this topic ...
Based on my understanding/ on what I understand, here's what I think ...

When it's opportunity to learn.

That's a great question. Let's look into it together.
Let's see if we can figure that out together.

You need more details to give the right answer.

Before I answer that question, could you provide some more details?
Before you answer that, could you clarify what you mean?

Casual situations.

I don't have the foggiest idea.
I don't have the clue. 
Don't ask me.
Who knows?
Your guess is as good as mine.