How much of the fees a professional services firm earns do the professionals get?

I think I once read (but I might remember incorrectly) that in the IB industry, approx. 50% of the fees earned are paid as compensation to the bankers.
Would you agree to this 50% rule of thumb?
More generally, is there a rule of thumb that may appy to most professional services firms (banks as well as law, consulting, accounting firms etc.) that x% of fees earned by the professionals is paid aout as compensation?

Thanks,
Philipp