Hi Oleg,

The amount you can contribute into a Solo 401k is a function of your net self-employment earnings and how much you contribute to retirement plans offered by other employers where you work. Once you max out the Solo 401k, you can't put away more money, even if you declare those contributions as non-deductible.

That being said, I'm not sure that I answered your question. You can set up your SOLO 401k to accept Roth Contributions. That means you won't get a deduction for those contributions, but they will grow tax-free. It's my understanding that you can only set up the "salary deferrals" to be classified as Roth contributions. The maximum salary deferrals are $18k if under 50, and $24k if 50 or older. You need to combine salary deferrals of all your employers when determining the max you can contribute. The remaining $35k that you can put away into the Profit Sharing Plan portion of the Sole 401k would be pre-tax.

Hope this answers your question.

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