So, fine with me is the standard way to say it.
But fine by me is ok, and dictionaries confirm that. The only mention that it should not be used is here: https://english.stackexchange.com/a/37205/19577
- But what is the background of fine by me? Is it rude/redneck/chav/kid/archaic/odd ?
- What would be an impression about the speaker, when the person is using fine by me?
- Can you use it in business correspondence ?
Best Answer
"Fine with me" is more formal than "Fine by me" but only by a little bit.
I doubt I would use either expression in a business document. Why? Because the expression basically has no meaning in a business sense. It is like calling something "very nice".
In a Business sense I would probably use the word "acceptable". "Fine by me" and "fine with me" are more common speech terms.
For example:
The contract details as defined in your document are acceptable to me.
The contract details as defined in your document are fine with me.
The contract details as defined in your document are fine by me.
The last example makes me think it was written by my teenaged son. The middle one is not bad, but what does "fine" mean? The first one clearly says the details are actionable, the contract can move forward.