Side Income and Self-Employment Tax

Side income is one of the most powerful accelerators available to a family building wealth — and it comes with tax obligations most people meet for the first time when a 1099 lands in the mailbox.

What Counts as Earned Income

Two flavors. W-2 income: an employer withholds your taxes and sends you a W-2. Self-employment income: everything else you’re paid to do — freelancing, consulting, lawn care, tutoring, Etsy, rideshare, reselling, monetized content. Both are earned income in the IRS’s eyes, which is exactly what makes them special: earned income is the key that unlocks IRA contribution room, including the Roth IRA for minors. Gifts, allowance, and investment gains are not earned income, no matter how industrious the recipient.

For a child or teen, that unlocking comes with a filing rule most families get wrong. A teenager can earn up to the standard deduction in W-2 wages ($16,100 for 2026) and owe nothing, but self-employment income is measured against a completely different and much lower bar: $400 of net earnings triggers a required return. The full teen picture — thresholds, the W-4, and how to keep the records that prove it — is in How a Teen Fills Out a W-4.

Self-Employment Tax: The 15.3% Surprise

At a W-2 job, you pay 7.65% FICA and your employer quietly pays the other 7.65%. Work for yourself and you are both parties: 15.3% self-employment tax on net earnings, on top of income tax, once you clear just $400 for the year.[1] You do get to deduct the “employer half” on your 1040, but the practical rule is simpler: set aside 25–30% of every gig payment the day it arrives, in a separate savings account, and tax season becomes a transfer instead of a crisis.

Quarterly Estimated Payments

The tax system is pay-as-you-go. An employer does it via withholding; the self-employed do it via quarterly estimated payments (April, June, September, January) once you expect to owe $1,000+ for the year.[2] Miss them and the IRS adds an underpayment penalty — not catastrophic, but pure waste. If side income supplements a day job, the painless alternative is raising withholding at the W-2 job to cover the gig taxes: one W-4 tweak, no quarterly calendar.

Records, Deductions, and the 1099s

Every legitimate business expense — supplies, mileage, software, the mower blade — reduces the profit you’re taxed on, but only if it’s written down. A spreadsheet with date, payer, amount, and expenses is enough at side-hustle scale (our income tracker works for adults too). For a teen running a first venture, the purpose-built version is the Teen Self-Employment Ledger, walked through with two worked examples in How a Teen Tracks Side-Hustle Income. Platforms send a 1099-K above $20,000 and 200 transactions; clients send 1099-NECs at $600+ — but the obligation to report income exists with or without the form. Report it all; the records are also what prove Roth eligibility for a teen’s cash income.

Side Income Across the Family

For teens, self-employment income is often the only earned income available before 14 — and with traditional summer jobs at historic lows, it’s frequently what funds the first custodial Roth IRA.

For parents, a real side business opens serious doors: business deductions, a SEP-IRA or Solo 401(k) with contribution room up to $72,000 (2026), and the option of legitimately employing your own kids. When the hustle grows into a company, the roadmap is From Tradesman to Owner.

Final Thought

Side income punishes the disorganized and rewards the record-keepers, at any age. Set aside the percentage in a separate account just for tax payments, log every payment, pay the quarters (or fix the W-4), and route what you can into tax-advantaged accounts. The extra income is nice; the extra options are the real product. For a teen starting from zero, the ledger and two worked examples are in How a Teen Tracks Side-Hustle Income — and note that self-employment income earns no unemployment insurance coverage, which is one more reason the cash cushion matters.