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Turbotax double taxing my after-tax contribution on Mega Backdoor Roth IRA when combined with pre-tax to roth IRA conversion



I'm getting wrong numbers (double taxing my after-tax non-roth contributions) from Turbotax after inputting megabackdoor roth IRA and Roth IRA conversion/rollover of an employer sponsored pretax retirement plan, so I'm posting here for your help. 


I was an employee of the University of California system that sponsors defined contribution plan (DCP), similar to 401K. It has a mandatory monthly pre-tax contribution component and voluntary after-tax non-roth contribution that can be rolled over monthly to Roth IRA (aka Mega Backdoor Roth IRA). I switched job in the middle of year 2020, which allowed me to rollover the pre-tax component of the DCP into Roth IRA (in addition to my monthly mega backdoor roth IRA). 


To summarize, DCP account has the following components for tax purposes:

1. Pre-tax Contributions + associated earnings (which was rolled over to roth IRA at the end of employment - taxable) 

2. After-tax non-roth contributions (which got converted to roth IRA every month - should not be taxed)

3. Earnings on After-tax non-roth contribution (taxable and rolled over to roth IRA)


I got my 1099-R form from Fidelity and here it is. 

1. Gross distribution $12,106.56

2a. Taxable amount: $6,028.31

2b. Total distribution checked

5. Employee contrib/desig Roth contrib or insurance premiums: $6000 (this was the amount of after-tax non-roth contribution that I made before its associated earnings)

7. Distribution code: G


When I plug these numbers in to Turbotax, the 1040 form shows:

5a Pensions and annuities: $12,107

5b Taxable amount: $12,135

which is likely incorrect because it seems to count the $6000 non-roth after tax contribution as taxable amount. 


This was how I plugged my information into turbotax: 

-On the form 1099-R you received, is the IRA/SEP/SIMPLE box between box 7 and box 8 checked? ans: no the box is blank

-Is this 1099-R reporting a rollover of funds from a 401k plan to a designated roth 401K? ans: No, this money didn't roll over to a designated roth 401k

-For rollovers to a Roth IRA, we may need to collect additional info. For rollovers to all other types of retirement account (such as traditional IRA), just answer No. ans: Yes, this money was rolled over to a Roth IRA account

-Did you make any after-tax contributions to your 401k plan? This would be contributions you made into the plan yourself, rather than being made by your company on your behalf. ans: yes, I made after-tax contributions to this 401k.

-After tax contributions to 401K: ans: $6,000.00

-Was this pension received from employment as public safety officer? ans: No


What am I doing wrong? How do I make it so that I don't get double taxed on my after-tax contribution of 6000?


Thanks for your help.

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