As a self-employed person, you can set up your own 401k plan with minimal expense and hassle. You can put in the 401k limits (including catch-up limits for people who are at least age 50, which totals $16,000 this year) up to your earned income. You can then also make an "employer" contribution up to 25% of earned income. Many brokerage firms offer these. As a self-employed attorney, my individual 401k is with Fidelity. You don't have to file any plan reports until your plan holds over $100K, and most of the brokerages will handle this for you for a minimal fee. You can also do it yourself, it is easier than preparing your own taxes.
Settting up the 401k is great if it allows you to put aside more money than you can in a SEP-IRA. The SEP is even easier to set up, but you are limited to contributions equal to 25% of earned income. It just depends on how much you have available to save and how much trouble you want to go to. Fidelity has a SEP-IRA contribution calculator on its website that will show you how much you can save based on your income and expenses.
The approach I have described works best if you are a sole proprietor. There are some differences if you are an employee of your own corporation.
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