key is Schedule C

To make rental into active income you have to
(1) organize an LLC,

(2) quitclaim all income generating properties to LLC

(3) report profit/loss on Schedule C
www.irs.gov/uac/Schedule-C-(Form-1040),-Profit-or-Loss-From-Business

Note: schedule C requires active income (earned income), not capital gain when you buy/sell houses (passive income). Rental income might include both active/passive income, so see here for how rental income is treated under schedule C

www.irs.gov/publications/p527/ch03.html

which says:  "In most cases, all rental real estate activities (except those of certain real estate professionals, discussed later) are passive activities."

(4) if you actually had a profit, you can open up a solo 401(k).


My guess is you can't do it because most of your rental income are passive incomes.