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As a former State of California emplyee SavingsPlus allows me to have a 457 with Charles Schwab. Recently I asked their help desk if I could move 40K to a Schwab IRA Roth. The contact person said it may be done via a "conversion".
I needed to sell 40K of my Schwab Total Stock, put it in a money market where it moves back to SavingsPlus.
Once this is done it goes back to the same Schwab account but SavingsPlus establishes a "ratio" of pre-tax and post-tax funds.
SavingsPlus sends me a tax form and I pay the taxes on the 40K.

Can someone explain how this is feasible?

Thank you.