Employer Tips on Contribution Designation & Mega Backdoor Roth

[Shiv P.]

Hi team,

A few time-sensitive questions given the Sept 15 S-corp extension deadline.

1) TRADITIONAL VS. ROTH DESIGNATION

I wired $5,076.92 (25% of my 2025 W-2 wages of $20,307.69) from my business account into my Solo 401(k) as an employer profit-sharing contribution. The wire cleared this morning (9/14) and shows up in 1 of the 3 Fidelity non-prototype accounts you helped set up (the other 2 currently show $0). That account doesn’t display a Traditional or Roth label. Has this contribution already been internally allocated/characterized as Roth in your records, or is it still open to designate as Traditional? How do I make or confirm that designation?

2) ACCOUNT LABELING PROCESS

Nothing in account setup let me designate which of the 3 accounts is Pre-tax, Roth, or Voluntary After-Tax. I saw an article suggesting we just nickname the Fidelity accounts. Is that genuinely the official mechanism for tracking contribution type, or is there a separate election/form on your end that actually governs this?

3) REVERSIBILITY — TWO SEPARATE QUESTIONS

(a) Can the $5,076.92 be recharacterized from Roth to Traditional (or vice versa), if it hasn’t been formally allocated yet?

(b) Separately — can the entire $5,076.92 employer contribution be unwound and returned to my business account, so I could instead treat the full $20,307.69 (100% of wages) as a single Voluntary After-Tax contribution instead? I understand (a) and (b) likely have very different answers — please address both.

4) MEGA BACKDOOR ROTH FOR THE REMAINDER

Assuming the $5,076.92 stands as an employer contribution either way: my 2025 W-2 wages were $20,307.69, so I believe I have $15,230.77 remaining room for a Voluntary After-Tax contribution ($20,307.69 − $5,076.92). Can you confirm?

If confirmed:

(a) Can this be funded from my personal account rather than the business account?

(b) What’s the correct account structure — one of the 2 empty accounts? Does it need to be separate from wherever the in-plan Roth conversion lands?

(b) What are the exact steps, in order, to fund it and then process the in-plan Roth conversion?

5) TIMING

The wire only cleared this morning and the deadline is tomorrow (9/15). Is it realistically possible to complete the Voluntary After-Tax contribution AND the in-plan Roth conversion by then? Is there any grace period beyond 9/15 for either step?

6) A FEW MORE DETAILS TO CONFIRM
(a) To avoid pro-rata complications on the eventual Roth conversion, should the Voluntary After-Tax contribution sit in a sub-account entirely separate from any pre-tax funds?

(b) When will the Form 1099-R be issued for whichever piece ends up taxable, and for which tax year?

Thanks so much — I know this is a lot.

Shiv P.

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