I'm looking at either a SEP IRA or a solo 401k plan to reduce taxes on the income I get from my single-member LLC side business (I also am a W-2 employee of a different company). I already max out my 401k contributions at my W-2 employer. Because the maximum employee contribution is aggregated across all 401k plans, I believe that for a solo 401k the only contribution I could make is the employer profit sharing amount, which would be the same as the maximum SEP IRA contribution (roughly 20% of the single member LLC income). However, when I run the numbers in TurboTax and select "maximize contribution" it says that for 2018 my max contribution to a solo 401k would have been substantially higher than the SEP IRA amount. It looks like it is ignoring the fact that I contribute to another 401k. Does TurboTax not correctly calculate the maximum solo 401k contribution if you have a separate W-2 employer 401k?
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