If you file Schedule C, you are a sole proprietor. A single member LLC that has not made the election to be a corporation is a sole proprietorship.
View on TurboTax's Keogh, SEP and SIMPLE Contribution Worksheet the calculation of your permissible solo 401(k) contribution.
"There have been many changes to the tax laws in the last several years."
None of those changes apply to this situation.
