Summary: Whether Polymarket winnings are taxable in the UK depends on how HMRC classifies your activity. Casual traders may qualify for the gambling exemption (tax-free). Systematic traders likely face Income Tax or Capital Gains Tax. HMRC's position on crypto prediction markets is still developing — document everything.
The UK tax treatment of Polymarket winnings is one of the most frequently asked questions among British prediction market traders. This guide covers the current HMRC position on Polymarket tax UK as of 2026, based on published HMRC guidance on cryptoassets and gambling winnings.
⚠️ Not tax advice. Tax positions depend on individual circumstances. Consult a UK-qualified chartered accountant or tax adviser for personalised guidance.
Three Possible Tax Treatments
HMRC has not issued specific guidance on prediction market contracts. Based on existing HMRC rules for cryptoassets and gambling, there are three possible treatments:
Treatment 1: Gambling Winnings (Tax-Free)
If HMRC treats your Polymarket activity as gambling, winnings are exempt from UK tax under existing gambling exemptions. This is the most favourable outcome and potentially applicable if:
- Your trading is occasional and not systematic
- You do not treat it as a primary or supplementary income source
- Your activity resembles consumer gambling rather than investment activity
Traditional UKGC-licensed betting (Betfair, Smarkets) clearly qualifies as tax-free gambling. Polymarket is crypto-denominated and sits outside the Gambling Act — HMRC may not apply the same exemption automatically.
Treatment 2: Capital Gains Tax (CGT)
HMRC's Cryptoassets Manual classifies most cryptoasset disposals as capital events subject to CGT. Under this treatment:
- Each winning trade is a disposal of USDC at a gain
- CGT rates: 18% (basic rate taxpayer) or 24% (higher/additional rate) from April 2024
- Annual exemption: £3,000 (2026/27) — gains below this are tax-free
- Losses can be offset against gains
- USDC received as settlement counts as disposal proceeds
Under CGT treatment, small-scale traders with gains under £3,000 per tax year pay nothing. Larger traders would report on Self Assessment under the Cryptoassets section.
Treatment 3: Income Tax (Trading Income)
If HMRC decides your Polymarket activity constitutes a trade, winnings are income subject to Income Tax:
- Tax rates: 20% (basic), 40% (higher), 45% (additional)
- National Insurance may also apply if self-employed
- Losses in trading years can be carried forward against future trading income
- Likely applies if: trading is systematic, frequent, occupies significant time, is a primary or secondary income source
HMRC's Published Guidance on Cryptoassets
HMRC published its Cryptoassets Manual (CRYPTO) in 2022 and updated it in 2024. Key points relevant to Polymarket:
- USDC as a stablecoin is a cryptoasset — subject to CGT on disposal
- Using crypto to purchase tokens/contracts may be a taxable event (disposal of USDC)
- HMRC does not currently have a specific category for prediction market contracts
- HMRC's 2025 cryptoasset reporting requirements mean UK exchanges must report user transactions — HMRC is building a data picture
Practical Record-Keeping for UK Polymarket Traders
Regardless of which tax treatment ultimately applies, keep these records:
- Date of each deposit: GBP amount, USDC received, exchange rate used
- Each market position: date opened, USDC staked, date resolved, USDC received
- Date of each withdrawal: USDC amount, GBP received, exchange used
- Annual summary: total USDC deposited, total USDC withdrawn, net gain/loss in GBP
Koinly and CoinTracker both support Polymarket/Polygon transaction import and generate HMRC-compliant CGT reports automatically.
The Gambling Tax-Free Argument in Practice
Some UK Polymarket users argue their winnings are gambling winnings and therefore tax-free, drawing an analogy with Betfair Exchange (which is clearly tax-free). The argument has merit for casual users but faces two obstacles:
- Polymarket is not UKGC-licensed — HMRC has not confirmed the gambling exemption extends to unlicensed overseas platforms
- The crypto nature of transactions means HMRC sees them as cryptoasset disposals, not gambling
Until HMRC issues specific guidance, the safest approach is to report under CGT and include a note explaining the gambling-exemption argument as an alternative position.
Reporting Polymarket Winnings on Self Assessment
If you need to report (gains over £3,000 or income over £1,000):
- Complete Self Assessment SA100 (or online via HMRC Personal Tax Account)
- For CGT: complete SA108 — declare disposals of cryptoassets in the "Other property, assets and gains" section
- For trading income: complete SA103 (self-employment) or SA800 (partnerships)
- Submit by 31 January following the tax year end
FAQ — Polymarket Tax UK
- Do I need to tell HMRC about small Polymarket winnings?
- If your total capital gains from all sources (including USDC trades) are under £3,000 in 2026/27, you do not need to report. If you are a basic rate taxpayer with gains under £3,000, no tax is due and no reporting is required.
- Are losses on Polymarket tax-deductible?
- Under CGT treatment, yes — losses can be offset against capital gains in the same or future tax years. Under trading income treatment, losses can also offset other trading income. Keep records of all losing positions.
- Does HMRC know about my Polymarket activity?
- HMRC's 2025 cryptoasset reporting requirements mean UK-regulated exchanges (Coinbase UK, Kraken) report user transactions above £1,000 per year to HMRC automatically. Transactions identifiable as prediction market activity may trigger HMRC enquiries for non-declarers.