The first thing to understand about side income in the US is that there is no tax-free allowance for it. Income is generally reportable regardless of the amount, and whether or not anyone sends you a tax form. Reporting thresholds determine when a payer has to send you a form — they do not determine when income becomes taxable.
Self-employment tax and the $400 threshold
If your net self-employment earnings are $400 or more in a tax year, you must file a return and pay self-employment tax, which covers both the employee and employer share of Social Security and Medicare. This applies even if your total income is otherwise below the filing threshold. Half of the self-employment tax is deductible when calculating your adjusted gross income. Income tax is separate and depends on your total income for the year.
Forms you may receive — and what they mean
- Form 1099-NEC: sent by clients who paid you $600 or more for services during the year.
- Form 1099-K: sent by payment apps and online marketplaces reporting gross payments once federal thresholds are met. Those thresholds have changed in recent years, so check irs.gov for the current figure. A 1099-K reports gross payments before fees, refunds and shipping, so it will usually be higher than your actual profit.
- Form 1099-MISC: used for certain other payments including rents and prizes.
- Receiving no form does not make the income untaxable. Not receiving a 1099 simply means the payer was not required to send one.
Reporting self-employment income
Self-employment income and expenses are reported on Schedule C with your federal Form 1040, and self-employment tax is calculated on Schedule SE. Your profit — income minus allowable business expenses — is what gets taxed, not your gross receipts. Most states with an income tax require the income to be reported on the state return as well.
Quarterly estimated tax
Nobody withholds tax from self-employment income, so the IRS expects you to pay as you go through quarterly estimated tax payments. Missing them can result in an underpayment penalty even if you pay the full amount when you file. If you also have a W-2 job, an alternative is to increase withholding on that job to cover the side income. Check irs.gov for the current due dates and safe harbor rules.
What you can deduct
Ordinary and necessary business expenses are deductible: equipment, software and subscriptions used for the business, supplies, professional fees and memberships, business insurance, advertising, and business mileage at the IRS standard mileage rate (commuting to a regular job does not count). A home office is deductible if the space is used regularly and exclusively for business, using either the simplified square-footage method or actual expenses. Personal expenses are not deductible, and mixing personal and business spending in one account is the fastest way to lose a deduction in an audit.
Selling personal items
Selling your own used possessions for less than you paid generally produces no taxable income, because it is a loss — and personal-use losses are not deductible either. Selling an item for more than you paid produces a reportable gain. Buying items specifically to resell at a profit on a regular basis is a business, and the profit is taxable. Because a 1099-K reports gross payments regardless of whether you made a gain, keep records of what you originally paid for items so you can show the position if asked.
Setting aside money for tax
The most common mistake new freelancers make is spending the full payment as it arrives. Setting aside 25% to 30% of profit in a separate account from the first payment is a sensible default — your actual rate depends on your total income, filing status and state — and paying quarterly estimates from that account turns tax from a shock into a routine.
A worked example
Suppose you earn $8,000 from freelance work alongside a W-2 job. Business expenses: software $300, equipment $200, home office $400 — total $900. Net profit: $7,100, reported on Schedule C. Because net earnings exceed $400, self-employment tax applies on Schedule SE, and half of it is deductible against your adjusted gross income. The $7,100 also stacks on top of your employment income for income tax purposes, so it is taxed at your marginal rate — which is why a side income can feel more heavily taxed than expected. Between self-employment tax, federal income tax at your marginal rate and any state income tax, setting aside 25% to 30% of profit is a reasonable planning assumption.
Key dates
- The US tax year is the calendar year, ending December 31
- Quarterly estimated tax payments are generally due in April, June, September and the following January — check irs.gov for exact dates each year
- Federal returns are generally due in mid-April, with an extension available to file (but not to pay)
- 1099-NEC and 1099-K forms are generally issued to you by the end of January
- Penalties apply for late filing and late payment, and they are calculated separately
Free filing help
IRS Free File at irs.gov/freefile offers free guided tax software below an income threshold, and free fillable forms above it. The VITA program offers free in-person preparation for people who qualify by income, disability or limited English, and many VITA sites handle straightforward Schedule C returns. TCE offers free help focused on taxpayers aged 60 and over. Find sites through irs.gov. Paying for preparation is worth it once your situation gets complicated, but check the free options first.