The answer depends on the ownership structure of the two businesses which determines whether or not these businesses are a controlled group and are therefore considered to be a single employer. If they are considered to be a controlled group, the businesses are considered to be a single employer with regard to retirement plans. If you are 100% owner of your sole proprietorship and your LLC is a single-member LLC, these must be treated as a single company and your net earnings from self-employment income will be determined by aggregating these two businesses.
See the following discussion of controlled and affiliated service groups: <a rel="nofollow" target="_blank" href="
https://www.irs.gov/pub/irs-tege/epchd704.pdf">https://www.irs.gov/pub/irs-tege/epchd704.pdf</a>
If these businesses are not members of a controlled group, they can be treated as separate businesses with separate retirement plans (or lack thereof). TurboTax does not support determining the permissible contributions when multiple separate businesses are involved.
