Do Prediction Market Profits Trigger Self-Employment Tax or the 3.8% NIIT?

Most prediction market traders don't owe self-employment tax, because capital gains are excluded and an investor isn't running a business. Professional gamblers are the main exception. The 3.8% net investment income tax is a separate question: it can apply to capital-treatment gains once your modified AGI passes $200,000 single or $250,000 joint. How NIIT applies to gambling or other-income treatment isn't addressed by the IRS, so those rows are less certain.

OddsFile is software, not tax advice. The IRS has not issued guidance on how prediction-market contracts are taxed. This article explains the options and the sources behind them; a tax professional can tell you which position fits your situation.

At a glance

Self-employment tax

The tax is 15.3%, split into 12.4% Social Security and 2.9% Medicare, if you have net earnings from self-employment of $400 or more. The Social Security part stops at the 2026 wage base of $184,500.

It applies only to a trade or business, and Section 1402(a)(3) excludes gain or loss from the sale or exchange of a capital asset. So:

• Investors: no business, no self-employment tax.
• Traders: Publication 550 says gains and losses from selling securities or commodities as a trader aren't subject to self-employment tax, with or without a Section 475 election. Section 1402(i) has an exception for options and commodities dealers trading Section 1256 contracts.
• Professional gamblers: Publication 525 says gambling as a trade or business is considered self-employment.

Market makers and reward farmers

If you're quoting all day for Polymarket liquidity rewards, the rewards may be business income, even if your trading gains are not. Publication 550 notes that digital assets received by a contractor for services constitute self-employment income. Whether your quoting is a service to Polymarket, or simply trading, is not settled. The amount and how you run it matter.

The 3.8% NIIT

Topic 559 sets the tax at 3.8% on the lesser of your net investment income or the amount by which modified AGI exceeds the threshold:

The IRS says these amounts are not indexed for inflation. You figure it on Form 8960, and the IRS says it's subject to estimated tax.

What counts

Section 1411(c) and Topic 559 include interest, dividends, rents, passive income, income from a business of trading in financial instruments or commodities, and net gains from disposing of property. Wages and active business income don't count.

Applied to your year:

• Capital treatment: net gains from property are the core of NIIT. If your position is that a contract is a capital asset, assume it's included.
• Kalshi interest: interest is on the list.
• Trader status: the trading business category uses the Section 475(e)(2) definition of commodities, so it depends on the same unresolved question about whether event contracts are commodities.
• Gambling winnings: they aren't named in the statute, and the IRS NIIT questions and answers don't mention them. Many read that as excluded. No official source says so directly for event contracts.
• Other income: a net figure on line 8z is not on the list by name, but a position that this income escapes NIIT because of how you labeled it is weak if the economics look like gains.

A gambling trap

Even if winnings aren't investment income, they increase your AGI. Gambling treatment puts gross winnings on Schedule 1, and losses come off only on Schedule A, which doesn't reduce AGI. That can lift your modified AGI past the threshold, and NIIT then falls on your other investment income, such as dividends.

Worked example

Single filer, capital treatment. Wages of $170,000 and a $90,000 net short-term gain. Modified AGI is $260,000.

Now the same trader with $250,000 of wages and a $30,000 gain has NIIT on the full $30,000, or $1,140, because the gain is smaller than the excess.

Professional gambler example

On a Schedule C net of $25,500, self-employment tax is about $3,603. For an investor with the same economic profit under capital treatment and income below the NIIT threshold, the extra tax is zero. That's a real cost of claiming business status.

How to plan

1. Work out your modified AGI before any trading.
2. If you're near a threshold, model it under each treatment. Gross winnings can move you over.
3. Add NIIT to your estimated tax if you expect it.
4. Keep your state's rules in mind. Those are separate.

Run the free OddsFile check: paste a Polymarket or Hyperliquid address and see your 2026 P&L under each treatment, no signup. It gives you the gross and net figures you need for these tests.

FAQ

Do I pay Social Security tax on Polymarket winnings?

Not unless your activity is a business whose income counts as self-employment, such as a professional gambler. Investor gains don't.

Do Kalshi profits count as earned income for an IRA?

Investor gains generally aren't earned income. If this matters for you, ask a preparer.

Does NIIT apply if my only income is prediction markets?

Only if your modified AGI exceeds the threshold.

Is NIIT included in the rates in my bracket?

No. It's an additional tax computed separately on Form 8960.