To preserve your ability to make tax-deductible retirement contributions for the current year, you only need to *open* the account before December 31. You can then wait until you know your final tax liability (up until the April tax deadline) to decide the exact amount to contribute.

If a 401(k) plan allows it, high earners can make after-tax contributions beyond standard limits and then convert those funds to a Roth account within the plan. This strategy bypasses typical Roth income limitations, creating a large, tax-free growth vehicle for retirement.

Once a Solo 401(k) plan's assets exceed $250,000, the owner must file Form 5500-EZ annually. Failure to do so incurs steep penalties of $250 per day, up to $150,000. While the form is simple, this compliance requirement is often overlooked, and regulatory enforcement has recently increased.

For business owners with high income and few or no employees, a defined benefit pension plan can offer significantly larger tax deductions than standard retirement plans like a 401(k), potentially allowing for write-offs exceeding half a million dollars.

Don't rush to form an S-Corp. The tax savings typically don't outweigh the added costs and complexity, like running payroll, until your business is generating at least $60,000 to $80,000 in profit. Before that, a sole proprietorship or standard LLC is often more efficient.

It's a common misconception that Solo 401(k)s offer the same robust ERISA creditor protection as corporate 401(k)s. Because they don't cover non-owner employees, they lack this enhanced protection, leaving assets with the same vulnerability as a standard IRA—a critical distinction for professionals in litigious fields.

The Mega Backdoor Roth strategy works perfectly for solo practitioners and owner-only businesses. A solo 401k plan is exempt from the complex compliance testing and administrative burdens that often prevent larger companies from offering the feature, making it an especially powerful and streamlined tool for the self-employed.

An LLC is a legal designation for liability protection, not a tax classification in the eyes of the IRS. By default, a single-member LLC is taxed identically to a sole proprietorship. To change this, you must proactively file to be taxed as an S-Corporation.

Many don't realize the $72,000 annual retirement contribution limit applies per plan, not per person. A solo practitioner with a side business can max out their primary employer's 401(k) and still contribute up to another $72,000 to a separate Solo 401(k) or SEP IRA, provided their side income is sufficient.