Summary: The tax status of Polymarket winnings under UK law hinges on HMRC's classification of your trading behaviour. Those who trade casually may benefit from the gambling exemption (no tax liability). Active or professional traders will likely encounter Income Tax or Capital Gains Tax obligations. HMRC's regulatory stance on crypto-based prediction markets continues to evolve — maintain comprehensive records.
Determining the correct tax treatment for Polymarket winnings in the United Kingdom remains a pressing concern for many British participants in prediction markets. This resource explains the current HMRC position on Polymarket tax UK during 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 released targeted guidance addressing prediction market contracts specifically. Drawing on established HMRC frameworks for cryptoassets and gambling, three distinct tax scenarios may apply:
Treatment 1: Gambling Winnings (Tax-Free)
Should HMRC classify your Polymarket participation as gambling, your winnings would be fully exempt from UK taxation under current gambling exemption rules. This outcome is most probable and potentially available when:
- Your engagement with the platform is sporadic and lacks systematic structure
- You do not regard it as a regular or auxiliary income stream
- Your conduct mirrors consumer-level gambling rather than professional investment
Established UKGC-regulated betting platforms (Betfair, Smarkets) unambiguously qualify for tax-free gambling status. 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 the majority of cryptoasset transactions as capital events liable to CGT. Under this framework:
- Each profitable position represents a USDC disposal generating a taxable gain
- CGT rates: 18% (standard rate payers) or 24% (higher/top rate) effective from April 2024
- Annual exemption: £3,000 (2026/27 tax year) — gains beneath this threshold incur no tax
- Offsetting losses against gains is permitted
- USDC received upon settlement qualifies as disposal proceeds
Applying CGT treatment, modest traders with annual gains beneath £3,000 face zero tax burden. Those with larger gains must declare them via Self Assessment under the Cryptoassets section.
Treatment 3: Income Tax (Trading Income)
Should HMRC determine that your Polymarket engagement constitutes a trade, your winnings become taxable income subject to Income Tax:
- Tax rates: 20% (standard), 40% (higher), 45% (additional)
- Self-employment National Insurance contributions may apply
- Trading losses in any year can be carried forward to offset subsequent trading profits
- Probable application if: activity is methodical, frequent, consumes material time, forms a primary or secondary income source
HMRC's Published Guidance on Cryptoassets
HMRC released its Cryptoassets Manual (CRYPTO) in 2022, with revisions published in 2024. Relevant considerations for Polymarket participants include:
- USDC, as a stablecoin, constitutes a cryptoasset — disposals trigger CGT
- Converting crypto to acquire market positions or tokens may constitute a taxable event (USDC disposal)
- HMRC presently lacks a dedicated framework for prediction market instruments
- New cryptoasset reporting obligations from 2025 require UK-based exchanges to furnish HMRC with transaction data — HMRC is assembling comprehensive intelligence
Practical Record-Keeping for UK Polymarket Traders
Whichever tax treatment ultimately prevails, maintain the following documentation:
- Deposit dates and amounts: GBP value transferred, USDC received, applicable exchange rate
- Individual market transactions: date position initiated, USDC committed, settlement date, USDC returned
- Withdrawal details: USDC quantity withdrawn, GBP equivalent received, exchange platform used
- Year-end reconciliation: cumulative USDC deposited, cumulative USDC withdrawn, overall profit or loss in sterling
Platforms such as Koinly and CoinTracker both facilitate Polymarket/Polygon transaction synchronisation and produce HMRC-compliant CGT documentation without manual intervention.
The Gambling Tax-Free Argument in Practice
Certain UK Polymarket participants contend that their returns constitute gambling winnings and merit tax-free status, referencing the established tax treatment of Betfair Exchange (unambiguously tax-exempt). This reasoning carries logical weight for occasional participants but encounters two significant hurdles:
- Polymarket lacks UKGC authorisation — HMRC has not confirmed whether the gambling exemption applies to unregulated international platforms
- The cryptoasset dimension of transactions means HMRC categorises them as cryptoasset disposals rather than gambling
Absent explicit HMRC guidance, the prudent course involves reporting under CGT whilst including commentary explaining the gambling exemption as a plausible alternative position.
Reporting Polymarket Winnings on Self Assessment
Where reporting becomes necessary (gains exceeding £3,000 or income surpassing £1,000):
- Complete the Self Assessment SA100 form (alternatively via HMRC's online Personal Tax Account)
- For CGT scenarios: complete SA108 — record cryptoasset disposals under the "Other property, assets and gains" category
- For trading income scenarios: complete SA103 (self-employed) or SA800 (partnerships)
- File by 31 January in the year following the relevant tax year
FAQ — Polymarket Tax UK
- Do I need to tell HMRC about small Polymarket winnings?
- Provided your combined capital gains across all sources (including USDC transactions) remain beneath £3,000 during 2026/27, notification to HMRC is unnecessary. For basic rate taxpayers with gains under £3,000, no tax liability arises and reporting is not required.
- Are losses on Polymarket tax-deductible?
- Under CGT treatment, absolutely — losses can be deducted from capital gains within the same or subsequent tax years. Under trading income treatment, losses similarly reduce other trading income. Retain documentation of all unprofitable positions.
- Does HMRC know about my Polymarket activity?
- From 2025 onwards, cryptoasset reporting obligations compel UK-regulated exchanges (Coinbase UK, Kraken) to disclose user transaction details exceeding £1,000 annually to HMRC. Transactions identifiable as prediction market engagement may prompt HMRC investigation if unreported.