Paper Check
One option would be to go to the local Schwab branch and make contributions by paper check (e.g. pre-tax contributions to the pre-tax account, voluntary after-tax contributions to the after-tax account, etc.)
Schwab won’t allow you to electronically transfer funds to the brokerage account from an external account not titled in the name of the plan.
If you make solo 401k contribution by check, use the following:
1. In the memo section of the contribution check, write the applicable Charles Schwab brokerage account number for the designated solo 401k.
2. On the back of the check sign your name. After you sign, write, Trustee of “list the name of your self-directed solo 401k” Then write For Deposit Only. Then write the Charles Schwab brokerage account number for the applicable solo 401k designated brokerage account. IMPORTANT Note: repeat the above for each check if you make multiple types of solo 401k contributions (i.e., Roth, pretax, voluntary after-tax)) so that the funds get deposited into the correct solo 401k brokerage account.
3. Then deposit the check(s) at the local Schwab branch, or overnight the check(s) to Schwab Operation Center located in one of the following centers depending on the closest location to you.
If you’re a resident of one of the following states: AK, AZ, CA, CO, HI, IA, ID, KS, MT, ND, NE, NM, NV, OK, OR, SD, TX, UT, WA, or WY, or a member of Armed Forces America or Armed Forces Pacific.
Overnight Mailing Address
Charles Schwab & Co., Inc.
El Paso Operation Center
1945 Northwestern Drive
El Paso, TX 79912
If you’re a resident of one of the following states: AL, AR, CT, DC, DE, FL, GA, IL, IN, KY, LA, MA, MD, ME, MI, MN, MO, MS, NC, NH, NJ, NY, OH, PA, RI, SC, TN, VA, VT, WI, WV, American Samoa, Guam, Marshall Islands, Northern Mariana Islands, Puerto Rico, or the Virgin Islands, or a member of Armed Forces Europe.
Overnight Mailing Address
Omaha Operations Center
200 S 108th Ave
Omaha, NE 68154
https://www.schwab.com/contact-us
Second Option
A second option is to open a brokerage account at Schwab in your name, fund the brokerage account in your name, and then transfer the funds from the brokerage account in your name to the brokerage account in the name of the plan (subject to the contribution limits, deadline, etc.).
