What's the tax difference between an LLC taxed as a sole proprietor and one taxed as an S-corp?

The legal entity is identical — the difference is purely how profit is taxed. An LLC taxed as a sole proprietorship (the default for a single owner) reports all profit on Schedule C, and the entire net profit is subject to ~15.3% self-employment tax plus income tax. An LLC that elects S-corp treatment instead splits profit into a reasonable W-2 salary (subject to payroll tax) and distributions (not subject to self-employment tax), which can cut your total payroll-type tax. The trade-off: the S-corp adds payroll, a separate business return, and accounting costs. So at low profit the default is simpler and cheaper overall; at higher profit the S-corp's tax savings can exceed those added costs. Same protection either way — you're choosing a tax treatment, not a different shield. Run both scenarios before electing.