How to pay the mandatory 20% federal tax amount on Solo 401k distributions: 

• 20% Mandatory Federal Tax Withholding Based on Distribution Amount: 20% for federal taxes that must be withheld at the time of Solo 401k distribution and submitted to the IRS electronically.
•  See the following link regarding this rule: http://www.mysolo401k.net/does-the-20-federal-tax-withholding-apply-to-all-401k–distributions/

• 15th of the Month: Must pay tax electronically by the 15th of the month subsequent to the month of your Solo 401k distribution date.
• Solo 401k EIN: Use the Employer Identification Number of your solo 401k when making the 20% Federal tax payment.
• Electronic: Electronic fund transfers are made using the Electronic Federal Tax Payment System (EFTPS).
• Tax Professional: If you do not want to use EFTPS, you can arrange for your tax professional, financial institution, payroll service, or other trusted third party to make deposits on your behalf. ( I recommend this method vs EFTPS since you don’t process a large number of distributions.)
• EFTPPS: EFTPS is a free service provided by the Department of Treasury. To get more information or to enroll in EFTPS, call 1-800-555-4477.
• You can also visit the EFTPS website at https://www.eftps.gov/eftps/Additional information about EFTPS is also available in Publication 966.
• Please also visit our website for tips on how to enroll in the EFPTS system: https://www.mysolo401k.net/enrolling-in-eftps-to-pay-taxes-due-on-solo–401k-taxable-distribution/
• Deposit record.   For your records, an Electronic Funds Transfer (EFT) Trace Number will be provided with your successful payment. The number can be used as a receipt or to trace the payment.
• Depositing on time.   For deposits made by EFTPS to be on time, you must initiate the deposit by 8 p.m. Eastern time the day before the date the deposit is due. If you use a third party to make a deposit on your behalf, they may have different cutoff times.
• Alternative Method: Same Day Taxpayer Worksheet: https://www.mysolo401k.net/same-day-taxpayer-worksheet-alternative-method-for-making-payment-of-the-solo-401k-20-mandatory-federal-tax-federal-tax-from-the-distribution/

Additional Reporting Applies to Solo 401k Distributions, which is your responsibility CLICK HERE to learn more.