Many people discover the $400 rule the wrong way — when they file their first freelance tax return and find they owe self-employment tax on what seemed like a small amount of income. Understanding this rule before you earn your first payment prevents that surprise.
The $400 threshold is one of the lowest filing triggers in the US tax code. It’s designed to capture even modest self-employment activity, because self-employed people pay both sides of Social Security and Medicare taxes. Here’s the full picture.
Where the $400 rule comes from
In standard employment, Social Security and Medicare taxes (collectively called FICA) are split between employer and employee. Each pays 7.65% on wages up to the Social Security wage base. The employee never sees the employer’s half — it’s paid separately.
As a self-employed person, you’re both. You pay 15.3% — the full FICA rate — on your net self-employment income. Congress set the $400 threshold as the minimum net self-employment income that triggers this tax obligation.
Compare that to the filing threshold for regular income, which is much higher ($14,600 for single filers in 2024 for most situations). You could have total income below the regular filing threshold but still be required to file because of $400 or more in net self-employment income.
What “net” means in this context
Net self-employment income is not what clients paid you — it’s what’s left after business expenses.
The IRS defines deductible business expenses as ordinary (common in your industry) and necessary (helpful for your business). Examples:
- Software subscriptions used for work
- Equipment purchased for the business
- A dedicated home office space
- Professional development expenses
- Travel directly for business purposes
If you earned $800 in freelance income and spent $500 on directly related business expenses, your net income is $300 — below the $400 threshold, no self-employment tax.
If you earned $800 with only $200 in expenses, your net is $600 — above $400, and you owe self-employment tax.
This distinction matters because some freelancers gross well above $400 but have high enough legitimate expenses that their net drops below it. And some gross below $400 in revenue but have negligible expenses, so their net is close to their gross.
The actual tax calculation on small self-employment income
Self-employment tax is 15.3% on 92.35% of net income (the 92.35% factor is a built-in adjustment equivalent to deducting half of self-employment tax before calculating it).
On $600 of net self-employment income:
- $600 × 92.35% = $554.10
- $554.10 × 15.3% = $84.78
So a freelancer with $600 in net self-employment income owes about $85 in self-employment tax, plus whatever federal income tax applies to that income at their bracket (which could be zero if their total income is low enough).
The amount is small, but the filing requirement is real.
When you might owe no tax but still must file
The filing requirement (triggered at $400 net self-employment income) and the tax liability (triggered based on taxable income and credits) are separate.
You might be required to file a return because of $400+ in net SE income, do the math, and find your total tax liability is zero after applying the standard deduction and credits. You still technically needed to file.
Practically, the IRS doesn’t send collection notices over $0 tax owed, but the filing requirement exists regardless.
Even if you don’t owe tax, filing when you have self-employment income protects you — it starts the clock on the statute of limitations for that year’s return.
Quarterly payments for the $400 threshold
If you expect to owe $1,000 or more in total federal tax for the year (income tax plus self-employment tax combined), quarterly estimated payments are required. For many freelancers earning modest amounts, the combined liability stays below $1,000, meaning quarterly payments aren’t technically required — but setting money aside is still smart practice.
If your freelance activity is a side project and you also have a W-2 job, you can adjust your W-2 withholding to cover both your employment and freelance tax liability. This is sometimes simpler than making separate quarterly payments. Ask your HR department to increase your withholding amount.
Side projects and the $400 rule
This rule catches freelancers who think of their work as too small to matter for taxes. If you sell a few designs, write a handful of articles, or take some photos for hire — and your net from those activities hits $400 — the filing requirement applies.
Many side-project freelancers discover this when they file using tax software for the first time. The software asks whether you received any self-employment income, they enter their small amount, and suddenly they have a self-employment tax liability they weren’t expecting.
The solution is simply to know the rule before you earn. Set aside 15–20% of any freelance payment, no matter how small, until you know what your net income for the year will be. For modest side income, even this small reserve is usually more than enough.
Use whatever tools you have to track your income — invoices, payment records, a spreadsheet. Staying on top of your total net SE income throughout the year means no surprises in April.
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