Small 1099 Income. Massive Tax Power.

Many doctors do medical surveys ($500/year), expert witness work ($5k/case), or medical directorships ($20k/year) and just throw the money into their checking account.

This is a mistake. By treating this active income as "hobby" income, you pay full marginal tax rates (37%+) on it.

If you earn money outside your W-2 employment — and you'll usually see it on a Form 1099-NEC in January — you have a side gig in the eyes of the IRS. For physicians, the list is longer than most people think:

• Paid medical surveys and market research panels
• Expert witness work — record review, depositions, testimony
• Chart review and utilization review for insurers
• Telehealth shifts paid as an independent contractor
• Medical directorships and advisory retainers
• Speaking and consulting for device or pharma companies
• Precepting stipends and moonlighting shifts paid on 1099

Two things matter here. First, this income is reportable whether or not the payer sends you a 1099 — a $400 honorarium paid by check still belongs on your Schedule C. Second, the moment you have legitimate business income, you have a business. No LLC, no paperwork, no permission required: Schedule C of your personal return IS the tax return for a sole proprietorship.

Here's a worked example. A hospitalist does $3,000 of surveys, one $6,000 expert witness case, and $9,000 of telehealth shifts in a year. That's an $18,000 business. Treated as loose "extra money" with no expenses claimed and no retirement contribution, it adds roughly $6,700 of federal income tax at a 37% marginal rate. Treated as a business — with a home office, a laptop, allocated license costs, and a Solo 401(k) — the taxable income from the same gig can shrink to a fraction of that, sometimes to zero.

Most people think retirement contributions are limited to a percentage of income. In a Solo 401(k), the "Employee" side allows you to contribute 100% of your compensation up to $24,500.

Scenario: You earn $20,000 reviewing legal cases.

Strategy: You contribute almost the entire $20,000 into your Solo 401(k) (assuming you haven't maxed your W-2 401k employee limit). The result? You pay basically $0 income tax on that side hustle.

Open A Solo 401(k)

Self-employment tax is 15.3% on paper — 12.4% Social Security plus 2.9% Medicare — but most attendings never pay anything close to that on side income. The Social Security portion only applies up to the annual wage base, and your hospital W-2 usually fills that bucket by itself.

What's left on your side-gig profit is the 2.9% Medicare piece, plus the 0.9% Additional Medicare Tax once your combined wages and self-employment income exceed $200,000 (single) or $250,000 (married filing jointly). Call it roughly 3.8% on net profit for a typical attending.

The bigger trap is timing. The IRS expects tax as you earn, not in April. The cleanest fix for most physicians is the safe harbor: pay in 110% of last year's total tax (the threshold that applies once your AGI exceeds $150,000) through withholding and estimates, and you won't owe an underpayment penalty no matter how big the side income grows.

An S-Corp saves self-employment tax by splitting profit into salary and distributions. But if your W-2 already covers the Social Security wage base, the only self-employment tax left to save is the roughly 3.8% Medicare slice — and an S-Corp adds payroll filings, a separate business tax return, and compliance costs that commonly run $1,500–$3,000 per year. On a $20,000 side gig, that math loses.

Where it flips: physicians clearing roughly $75,000–$100,000+ of net 1099 profit — full-schedule telehealth, heavy expert witness practices, or doctors who leave W-2 employment for locums entirely. At that level, entity structure, reasonable compensation planning, and retirement plan design start producing real dollars, and the compliance cost becomes a rounding error.

We cover the decision in detail in our moonlighting entity structure guide and our 1099 side gig strategy page. If you're not sure which bucket you're in, that's exactly what the discovery call is for.