Calculating earned income for a sole proprietor

[Guest RICHEZ]

Can anyone recommend any reference material for information on calculating earned income for a sole proprietor or partner in a 401k plan? We have a few clients in this situation. The complexity seems to rise significantly when they want us to calculate the maximum match for a partnership. This creates the ol' circular reference problem since their income is reduced by the match which is based on their earned income. Right now, I'm just looking for reference material. If any of you are interested in the gory details, email me.