In this guide
Summary: The tax position on Polymarket winnings in the UK hinges on HMRC's classification of your trading behaviour. Those engaging casually may benefit from the gambling exemption (no tax liability). Active or frequent traders are more likely to encounter Income Tax or Capital Gains Tax obligations. HMRC continues to develop its stance on decentralised prediction markets — meticulous record-keeping is essential.
Determining the correct tax treatment for Polymarket winnings remains a pressing concern for UK-based participants in on-chain prediction markets. This resource outlines the current HMRC position on Polymarket tax UK throughout 2026, drawing on official HMRC guidance regarding cryptoassets and gambling-related income.
⚠️ Not tax advice. Your specific tax position depends on your individual circumstances. Seek guidance from a qualified UK tax professional or chartered accountant for advice tailored to your situation.
Three Possible Tax Treatments
HMRC has not yet published definitive guidance on prediction market contracts. Drawing on established HMRC frameworks for cryptoassets and gambling activities, three potential tax outcomes exist:
Treatment 1: Gambling Winnings (Tax-Free)
Should HMRC characterise your Polymarket engagement as gambling, winnings would be entirely exempt from UK taxation under current gambling exemptions. This outcome is most advantageous and may apply where:
- Your participation is infrequent and lacks systematic structure
- You do not rely on it as a primary or secondary income stream
- Your behaviour aligns with consumer gambling patterns rather than investment conduct
Established UKGC-regulated betting platforms (Betfair, Smarkets) unambiguously qualify for tax-free gambling treatment. Polymarket operates on blockchain infrastructure and falls outside the Gambling Act framework — HMRC may decline to extend the same exemption without explicit confirmation.
Treatment 2: Capital Gains Tax (CGT)
HMRC's Cryptoassets Manual treats most cryptoasset transactions as capital disposals subject to CGT. Following this approach:
- Each profitable position represents a USDC disposal generating a taxable gain
- CGT rates: 18% (standard rate payers) or 24% (higher/additional rate) from April 2024
- Annual exemption: £3,000 (2026/27) — gains within this threshold incur no tax
- Offsetting losses against gains is permitted
- USDC settlement proceeds count as disposal consideration
Under CGT treatment, modest traders whose annual gains remain below £3,000 face zero tax liability. Larger-scale traders would declare transactions on Self Assessment under the Cryptoassets section.
Treatment 3: Income Tax (Trading Income)
Should HMRC determine your Polymarket engagement constitutes a trade, winnings become taxable income subject to Income Tax:
- Tax rates: 20% (standard), 40% (higher), 45% (additional)
- Self-employment National Insurance contributions may be payable
- Trading losses may be carried forward to offset subsequent trading income
- Likely triggered by: systematic approach, high transaction frequency, substantial time commitment, reliance as primary or secondary income
HMRC's Published Guidance on Cryptoassets
HMRC released its Cryptoassets Manual (CRYPTO) in 2022 with further updates during 2024. Relevant provisions for Polymarket participants include:
- USDC, as a stablecoin, qualifies as a cryptoasset — CGT applies upon disposal
- Deploying crypto to acquire tokens or contracts may constitute a taxable disposal event (USDC disposal)
- HMRC currently lacks a dedicated framework for prediction market instruments
- 2025 cryptoasset reporting obligations require UK-regulated platforms to furnish transaction data to HMRC — the authority is developing comprehensive transaction intelligence
Practical Record-Keeping for UK Polymarket Traders
Whichever tax framework ultimately governs your position, maintain comprehensive documentation:
- Deposit transactions: transaction date, GBP amount transferred, USDC received, applicable exchange rate
- Market participation: opening date, USDC committed, settlement date, USDC returned
- Withdrawal transactions: transaction date, USDC withdrawn, GBP equivalent, exchange platform used
- Year-end reconciliation: cumulative USDC inflows, cumulative USDC outflows, net gain or loss expressed in GBP
Platforms including Koinly and CoinTracker facilitate Polymarket/Polygon transaction tracking and produce HMRC-compliant CGT documentation without manual calculation.
The Gambling Tax-Free Argument in Practice
Certain UK Polymarket participants contend their returns constitute gambling winnings exempt from taxation, citing parallels with Betfair Exchange (which enjoys clear tax-free status). This reasoning holds some validity for occasional users yet encounters two substantive challenges:
- Polymarket operates without UKGC licensing — HMRC has not confirmed whether gambling exemptions extend to unlicensed international platforms
- The blockchain-based transaction structure leads HMRC to characterise them as cryptoasset disposals rather than gambling outcomes
Absent explicit HMRC direction, the prudent course involves reporting under CGT principles whilst documenting the gambling-exemption rationale as a secondary position.
Reporting Polymarket Winnings on Self Assessment
Where reporting obligations arise (gains exceeding £3,000 or income surpassing £1,000):
- Complete Self Assessment SA100 (alternatively via HMRC's online Personal Tax Account portal)
- For CGT: complete SA108 — enter cryptoasset disposals within the "Other property, assets and gains" category
- For trading income: complete SA103 (sole trader) or SA800 (partnership structures)
- Submission deadline: 31 January following the relevant tax year
FAQ — Polymarket Tax UK
- Do I need to tell HMRC about small Polymarket winnings?
- Provided your aggregate capital gains from all sources (encompassing USDC transactions) stay beneath £3,000 during 2026/27, notification is unnecessary. For basic rate taxpayers with gains under £3,000, neither tax liability nor reporting obligation exists.
- Are losses on Polymarket tax-deductible?
- Under CGT treatment, losses are deductible — they offset capital gains within the same or subsequent tax years. Under trading income treatment, losses similarly reduce other trading income. Document all unsuccessful positions meticulously.
- Does HMRC know about my Polymarket activity?
- 2025 cryptoasset reporting mandates require UK-regulated platforms (Coinbase UK, Kraken) to report user transactions above £1,000 annually to HMRC directly. Transactions identifiable as prediction market activity may prompt HMRC investigation if unreported by the taxpayer.