Polymarket tax UK: is it taxable, and what should you report?

Before anything else:this is not tax advice. HMRC's position on Polymarket-specific income isn't codified. Consult a chartered accountant for your personal circumstances. With that said — here's the landscape.

Is it legal to use at all?

Polymarket is geoblocked in the UK under its own Terms of Service. Accessing via VPN breaches the ToS (which could cost you your account and funds) but is not a criminal offence under UK law. The platform itself is not regulated by the UK Gambling Commission.

Are winnings gambling income?

UK domestic gambling winnings (bookmakers, lotteries, casino) are not taxable. HMRC treats them as windfalls. The question is whether Polymarket counts as “gambling” for HMRC purposes.

Polymarket doesn't fit neatly. It's a crypto-denominated contract settled in USDC, running on Polygon. HMRC is more likely to treat this as crypto-asset trading, bringing it under Capital Gains Tax (CGT). If the activity is frequent + systematic + profit-seeking, HMRC may reclassify it as trading income, which attracts Income Tax + NI (potentially up to 47%+).

The CGT angle in practice

• Each YES/NO contract buy-and-settle is potentially a disposal for CGT.
• Your cost basis = GBP-equivalent of the USDC spent at purchase time.
• Your proceeds = GBP-equivalent of the USDC received at resolution (or onwards sale).
• Annual CGT allowance for 2026: £3,000. Gains above that are taxed at 10-20% depending on your overall bracket.

What to document

1. Every on-chain transaction: deposit, each bet, each settlement, withdrawal. Block explorer links suffice.
2. GBP/USDC rate at each transaction time (coinbase / Binance historical is fine).
3. Net gain per tax year, calculated in GBP.

The safest play

Pay an accountant for a single hour. Show them your records. They might classify some portion as gambling (tax-free) and some as crypto gains (CGT). Far cheaper than the HMRC penalty for missed reporting, and you get peace of mind.

UK-regulated alternatives

If the tax + ToS friction is too much, consider UK-regulated exchange-style platforms (Smarkets, Betfair) where gambling winnings are tax-free domestically. They have worse odds on prediction events but the regulatory clarity is worth it for many users.