Summary: The UK tax position on Polymarket winnings hinges on HMRC's classification of your trading behaviour. Occasional participants may benefit from the gambling exemption (no tax liability). Regular or professional traders will likely encounter Income Tax or Capital Gains Tax obligations. HMRC's stance regarding crypto-based prediction markets continues to evolve — maintain thorough records of all activity.
Questions about UK taxation of Polymarket winnings rank among the most common concerns raised by British traders active in prediction markets. This guide examines the current HMRC position on Polymarket tax UK throughout 2026, drawing on official HMRC guidance concerning cryptoassets and gambling-related income.
⚠️ Not tax advice. Your specific tax position will depend on your individual circumstances and activity profile. 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 dedicated guidance addressing prediction market contracts specifically. Drawing on current HMRC rules governing cryptoassets and gambling activities, three distinct tax treatments emerge as possibilities:
Treatment 1: Gambling Winnings (Tax-Free)
Should HMRC classify your Polymarket participation as gambling, your winnings would be exempt from UK taxation under established gambling exemptions. This represents the most advantageous scenario and may apply when:
- Your trading occurs infrequently and follows no systematic pattern
- You do not rely on this activity as a main or secondary income stream
- Your behaviour aligns more closely with consumer gambling than investment trading
Conventional UKGC-authorised betting platforms (Smarkets, Betfair) unquestionably qualify as tax-exempt gambling. Polymarket operates via cryptocurrency 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 taxable capital events subject to CGT. This framework would operate as follows:
- Each profitable trade represents a USDC disposal generating a taxable gain
- CGT rates: 24% (higher/additional rate) or 18% (basic rate) since April 2024
- Annual exemption: £3,000 (2026/27) — gains beneath this threshold incur no tax
- Offsetting losses against gains is permitted
- USDC received upon contract settlement counts as disposal proceeds
Under a CGT framework, traders generating annual gains below £3,000 face no tax burden. Those with larger gains 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 would be classified as income subject to Income Tax:
- Tax rates: 45% (additional), 40% (higher), 20% (basic)
- Self-employment National Insurance contributions may be due
- Trading losses in any year can be carried forward and deducted from subsequent trading income
- Likely classification if: activity is systematic and regular, demands substantial time commitment, functions as a primary or secondary income source
HMRC's Published Guidance on Cryptoassets
HMRC released its Cryptoassets Manual (CRYPTO) in 2022, with subsequent revisions in 2024. Relevant considerations for Polymarket participants include:
- USDC, as a stablecoin, qualifies as a cryptoasset — CGT applies upon disposal
- Converting crypto to purchase market contracts or tokens may constitute a taxable disposal event (USDC)
- HMRC has not yet established a dedicated classification for prediction market contracts
- New cryptoasset reporting obligations in 2025 require UK exchanges to furnish HMRC with user transaction data — HMRC is assembling comprehensive transaction intelligence
Practical Record-Keeping for UK Polymarket Traders
Whichever tax treatment eventually applies, retain the following documentation:
- Each deposit date: GBP amount transferred, USDC received, applicable exchange rate
- All market positions: opening date, USDC committed, settlement date, USDC returned
- Each withdrawal date: USDC amount removed, GBP obtained, exchange platform used
- Year-end reconciliation: aggregate USDC deposited, aggregate USDC withdrawn, overall GBP gain or loss
CoinTracker and Koinly both facilitate Polymarket/Polygon transaction imports and produce HMRC-compliant CGT calculations without manual effort.
The Gambling Tax-Free Argument in Practice
Certain UK Polymarket traders contend their winnings constitute gambling income and therefore remain tax-exempt, comparing their position to Betfair Exchange (manifestly tax-free). This reasoning carries some weight for casual participants yet encounters two significant hurdles:
- Polymarket lacks UKGC authorisation — HMRC has not confirmed whether the gambling exemption covers unlicensed foreign platforms
- The cryptocurrency dimension means HMRC characterises transactions as cryptoasset disposals rather than gambling events
Absent specific HMRC pronouncements, the prudent approach involves reporting under CGT while appending a statement outlining the gambling-exemption argument as a secondary position.
Reporting Polymarket Winnings on Self Assessment
Where reporting becomes necessary (gains exceeding £3,000 or income surpassing £1,000):
- Submit Self Assessment SA100 (or file online through HMRC's Personal Tax Account portal)
- For CGT: complete SA108 — include cryptoasset disposals within the "Other property, assets and gains" category
- For trading income: complete SA103 (self-employment) or SA800 (partnerships)
- Deadline: 31 January following the conclusion of the tax year
FAQ — Polymarket Tax UK
- Do I need to tell HMRC about small Polymarket winnings?
- Should your combined capital gains from all sources (encompassing USDC transactions) fall below £3,000 during 2026/27, reporting is unnecessary. For basic rate taxpayers with gains beneath £3,000, no tax accrues and notification to HMRC is not required.
- Are losses on Polymarket tax-deductible?
- Under CGT treatment, absolutely — losses may be deducted against capital gains within the same or subsequent tax years. Under trading income treatment, losses similarly reduce other trading income. Preserve documentation for all unprofitable positions.
- Does HMRC know about my Polymarket activity?
- Beginning in 2025, cryptoasset reporting obligations compel UK-regulated exchanges (Kraken, Coinbase UK) to disclose user transactions above £1,000 annually to HMRC. Transactions identifiable as prediction market activity may prompt HMRC investigations if traders have not declared them.