Side income is still income. In the US, net profit from freelancing or gig work is generally subject to income tax and self-employment (SE) tax (Social Security and Medicare on net earnings). Planning ahead beats a surprise bill in April.
Know When You Owe SE Tax
If you earn $400 or more in net self-employment income (after expenses), you typically file Schedule C and pay SE tax unless an exception applies. Combine all side projects on one Schedule C when they are the same trade or business—ask a CPA if you run multiple distinct activities.
Deductions That Matter
Ordinary and necessary expenses reduce both income and SE tax: home office (strict IRS rules), software, equipment, mileage at the IRS rate for business miles, professional fees, and health insurance (self-employed deduction) in some cases. Keep receipts and a simple mileage log.
Pay Quarterly Estimated Taxes
If you expect to owe $1,000+ when you file, the IRS usually wants quarterly estimated payments to avoid penalties. Use Form 1040-ES or annualize income if your side hustle is seasonal. Withholding from a W-2 job can also be increased to cover side income.
Retirement and HSAs
A Solo 401(k) or SEP-IRA can defer taxes on a portion of profit. If you have a high-deductible health plan, an HSA offers triple tax advantages.
Conclusion
Open a separate business checking account, track profit monthly, and meet a tax pro once your side income grows. Use our Income Tax Calculator as a starting point for planning.