If you left an agency or in-house role to consult on your own, the biggest tax surprise is not the income tax, it is the payroll tax you now pay both halves of. Here is how it hits a consulting practice and what actually reduces it.
The 15.3% on retainers and project fees
As an employee, Social Security and Medicare cost you 7.65% of your paycheck while your employer quietly paid a matching 7.65%. As a self-employed marketing consultant, both halves are yours: 15.3% total, 12.4% for Social Security and 2.9% for Medicare, calculated on Schedule SE and paid with your Form 1040. It applies to your net profit, which means monthly retainers, campaign project fees, strategy sprints, and audit work all pool together on Schedule C, minus your business expenses, and the remainder owes the tax. The Social Security piece stops at an annual wage base the IRS adjusts each year; the Medicare piece keeps going on everything. This tax is owed in addition to ordinary income tax at your bracket, which is why the total bite on consulting profit shocks people in year one.
The $400 threshold and Schedule SE
The filing trigger is low: net self-employment earnings of just $400 for the year mean you must file a return and pay self-employment tax. There is no exception for side projects or for income under the $600 1099-NEC reporting line. A client who paid you $500 sends no form, and the income is still taxable; the 1099 threshold governs the client's paperwork, not your obligation. There is one silver lining built into the math: you deduct half of your self-employment tax as an adjustment to income, which lowers the income tax layer a bit.
One more note for consultants who incorporate: if you elect S corp taxation, your salary owes payroll taxes instead, and distributions above it escape the 15.3% entirely. That is a later-stage optimization once profit is consistently strong, not a day-one move.
Shrinking the bill with real deductions
Because the tax is charged on net profit, every legitimate business expense reduces it directly. For a marketing consultant that list is long: software subscriptions for analytics, design, scheduling, and reporting tools, contractors you bring in for design or copy, courses and certifications that keep your skills current, a qualifying home office, and travel to client engagements. A consultant grossing $120,000 who diligently tracks $25,000 of real expenses pays self-employment tax on $95,000, not $120,000; sloppy tracking literally costs 15.3 cents on every missed dollar, before income tax savings even start.
Because nothing is withheld from your invoices, plan on quarterly estimated payments covering both the income tax and self-employment tax layers. Set aside a percentage of every client payment when it lands and the Schedule SE line stops being an April emergency.