Yes, salary deferral and profit sharing contributions are generally 100% tax deductible. Roth 401k contributions made with the salary deferral portion of an Individual 401k are not tax deductible. Subchapter S and C corporations or LLCs electing to be taxed as a corporation can generally deduct the salary deferral contribution from personal W-2 earnings and the profit sharing contribution as a business expense.
A sole proprietorship, partnership or a LLC taxed as a sole proprietorship can generally deduct salary deferral and profit sharing contributions from personal income.