Home / Physicians & high earners / 1099 side income
1099 side income: the smallest business you will ever run — run it right
The short answer
Moonlighting shifts, expert-witness work, consulting — 1099 income makes you a business owner, which unlocks deductions, a Solo 401(k), and eventually the S-corp question. The order of operations: deduct properly first, add the retirement plan second, and elect S-corp only when consistent side profit clears roughly $60,000.
The order of operations
- Separate the money: dedicated account and card for the side gig.
- Take the real deductions: side-gig malpractice, allocable licensing, travel between sites, CME, genuine home office.
- Open the Solo 401(k): the employer layer (~20% of net side earnings) is available even if you max deferrals at your W-2 job.
- Run the S-corp math annually — our calculator gives the rough cut.
- Pay quarterlies on safe harbor so nothing is a surprise.
Hospitalist with $90k moonlighting profit
Where it goes wrong
- Electing S-corp on $30k of side income because a colleague did
- Missing the Solo 401(k) because of an existing 403(b)
- No separate account, so deductions evaporate at tax time
Frequently asked questions
At what point does side income justify an S-corp?
Same math as any business: consistent net profit around $60,000+ after expenses. Below that, a sole proprietorship with clean deductions usually wins on simplicity.
Can I open a Solo 401(k) on side income?
Yes — 1099 income makes you a business owner, eligible for your own Solo 401(k). The deferral limit is per person across all plans, but the employer layer on side income is yours even if you max deferrals at work.
What can I deduct against moonlighting income?
Ordinary and necessary costs of the gig: licensing fees allocable to it, malpractice for the side work, travel between sites, CME tied to it, home office where genuine, supplies.
Do I owe quarterly estimates on 1099 income?
Almost certainly — nothing is withheld. The safe-harbor method keeps it painless; our calculator does the math.
Moonlighting seriously?
One consultation maps your deduction set, opens the right retirement plan, and tells you honestly which side of the S-corp line you are on.
Book a free consultation