Proprietor has a normal SEP. My understanding is that the normal limits are 20% of income.
If instead a Simple IRA is established for 2004, I understand that they get a maximum of 10,000 plus 20% of income.( 11,000 income, over 50)
Maximum deduction of $12,700
Can this be set up now and contributions made before 04/15/2005

It is too late to establish a SIMPLE plan for 2004.

OTOH, a SEP can be established on or before the due date (generally, April 15) of the business's tax return for 2004.

If contributing 25 percent under a model or non-integrated prototype SEP, the owner's SEP contribution would be 20 percent [.25/1.25] of his or her net profits from SE [shown on "bottom line" of pre-plan Schedule C] after first deducting (a) any employee contributions made to the plan, and 1/2 of the self-employment tax deduction. After all reductions, the compensation limit is applied ($205,000 for 2004; $210,000 for 2005).

If the plan is integrated, this approach (the "equivalency method") does not work. Spreadsheet analysis/software is generally used in these situations.

…and I assume by “ proprietor you mean “Sole proprietor/unincorporated” right? Just checking, as many of our customers use the term even for small business owners whose businesses are incorporated. If the business is incorporated, you may already know that contributions would be up to 25% of W-2 wages from the business