Kentucky enacted the first state excise tax on prediction market transaction fees. A platform coalition sued June 12 to block it before a July 2026 restriction takes effect.
Kentucky became the first state in the country to tax prediction market transactions when Governor Andy Beshear's veto of House Bill 757 was overridden by the state legislature in spring 2026. Section 71 of HB 757 imposes a 14.25% excise tax on prediction market "transaction fees."
The Coalition for Fair Markets, representing Kalshi, Polymarket US, Crypto.com, and Robinhood, filed suit in Franklin Circuit Court on June 12 to block the measure before its effective dates. A provision barring state-licensed gaming operators from contracting with prediction market platforms takes effect July 2026. The transaction fee tax itself is set to take effect January 1, 2027.
The statutory definition matters. HB 757 defines "transaction fee" to include both the fee a platform charges to execute a trade and the amount a consumer pays to purchase an event contract directly from an operator.
On a CLOB-based exchange like Kalshi or Polymarket US, the practical target is the platform's taker fee. Here is the math on a $1,000 notional position at 50/50 odds.
| Platform | Taker Fee on $1,000 | 14.25% State Tax | Total Cost |
|---|---|---|---|
| Kalshi | $35.00 | $4.99 | $39.99 |
| Polymarket US | $20.00 | $2.85 | $22.85 |
Kalshi uses the fee formula: 0.07 × contracts × price × (1 - price). On 1,000 contracts at $0.50 each, that is 0.07 × 1,000 × 0.50 × 0.50 = $17.50 per leg, or roughly $35 round-trip. The Kentucky tax adds $4.99, pushing the all-in fee from 3.5% to 4.0% of notional.
Polymarket US charges a 2% taker fee. On $1,000 notional, that is $20. The Kentucky tax adds $2.85, lifting effective friction from 2.0% to 2.3%.
Run either scenario through the prediction market fee calculator to see how the additional state layer shifts your break-even win rate.
The statute's second clause creates a more severe scenario. If "amount paid by a consumer to purchase an event contract" is read as the full notional purchase price rather than the platform's fee, the tax becomes 14.25% on the full $1,000. That is $142.50 in additional state tax per $1,000 trade. At that level, prediction market trading is economically unworkable for Kentucky residents. The ambiguity in that definition is central to what the coalition is litigating.
The complaint in Franklin Circuit Court makes three distinct claims.
Federal preemption. The Commodity Exchange Act gives the CFTC exclusive jurisdiction over designated contract markets. HB 757 defines "prediction market operator" by direct reference to federal event contract law, meaning the state selectively taxes an activity Congress placed under federal authority. The coalition argues Kentucky cannot evade preemption by writing federal regulatory categories into its tax definitions.
Dormant Commerce Clause. Only CFTC-regulated exchanges (Kalshi, ForecastEx, Polymarket US) fall within HB 757's operator definition. Unregulated offshore platforms are not captured. The coalition argues this discriminates against legitimate, federally authorized interstate commerce while leaving noncompliant operators untouched.
Unequal treatment. Kentucky taxes horse racing transaction fees at approximately 9.75%. The 14.25% rate applied to prediction markets is 46% higher with no stated policy basis for the disparity.
Less than a week after the coalition filed, Kentucky Attorney General Russell Coleman opened his own action in Franklin Circuit Court. The AG's complaint targets Kalshi and Polymarket, alleging they operate unlicensed sports betting in violation of state law. The filing cited data showing that sports betting contracts represented approximately 70% of Kalshi's trading volume during a 2025 sample period.
Coleman's position is that prediction markets are sports betting under a different name, and that the CFTC's jurisdiction over derivatives does not displace Kentucky's authority to regulate in-state gambling.
The CFTC's own June 2026 proposed rulemaking is the relevant federal backdrop. The agency is formalizing when event contracts are contrary to the public interest, with a public comment deadline of July 27, 2026. How the CFTC defines the boundary between event contracts and sports wagering will directly shape how much room states have to act. The CFTC prediction market rules guide covers that framework in full.
The 14.25% tax is not yet in effect (effective date: January 1, 2027), and it applies to platform operators, not to individual traders directly. Kalshi and Polymarket US have not announced any Kentucky-specific fee surcharges as of June 19, 2026.
The nearer-term risk is platform-level access decisions. If the July 2026 provision triggers licensing concerns, platforms could restrict Kentucky residents before any court issues a temporary injunction. Monitor platform announcements in late June.
For federal tax treatment of prediction market winnings, the prediction markets tax guide covers how the IRS currently treats event contract gains and losses. The event contract tax treatment guide explains how CFTC-regulated contracts (Kalshi, ForecastEx) differ from offshore platforms (the original Polymarket) for reporting purposes.
Use the PM EV calculator to model how any fee increase changes the edge required to stay profitable. A 0.5 percentage point rise in platform friction on even-odds markets means your true probability estimate needs to be 0.5 points higher just to break even.