First of all only the Social Security part maxes out. You still pay the Medicare tax on both your W2 and self employment income. So if your W2 is over the max for SS you do not pay any SS on your self employment. I assume your SMLLC is NOT an S Corp? If it is a S corp I don't know how it works. Otherwise a SMLLC is filed on Schedule C in your personal return.
The SE tax includes what you already paid in from your W2 so your schedule SE tax will only be the difference up to the max amount of $9,932.40 for social security. The max for social security for 2023 is 6.2% of wages plus schedule C net profit up to $160,200. Medicare is 2.9% (both er & ee parts) of all wages & schedule C profit - no max.
You still might need to pay estimated payments to cover the income tax and Medicare tax on your self employment income.
