Polymarket Tax UK: HMRC Guide to Prediction Market Winnings 2026

Determining the correct tax position for Polymarket winnings in the United Kingdom remains a pressing concern for British participants in prediction markets. This resource examines the current HMRC position on Polymarket tax UK in 2026, drawing on official HMRC guidance regarding cryptoassets and gambling-related income.

Three Possible Tax Treatments

HMRC has not released targeted guidance addressing prediction market contracts specifically. Drawing on established HMRC frameworks for cryptoassets and gambling activities, three distinct tax outcomes are possible:

Treatment 1: Gambling Winnings (Tax-Free)

Should HMRC categorise your Polymarket engagement as gambling, your winnings would be fully exempt from UK taxation under the existing gambling exemption framework. This represents the most advantageous scenario and may apply where:

• Your market participation is infrequent and lacks systematic structure
• You do not rely on this activity as your main or secondary employment income
• Your behaviour aligns with consumer gambling patterns rather than investment conduct

Established UKGC-authorised betting platforms (Betfair, Smarkets) unambiguously qualify for tax-free treatment. 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. Under this framework:

• Every profitable trade represents a USDC disposal triggering a capital gain
• CGT rates: 18% (standard rate) or 24% (higher/additional rate) effective from April 2024
• Annual exemption: £3,000 (2026/27 tax year) — no tax on gains beneath this threshold
• Capital losses reduce taxable gains in the same or subsequent years
• USDC received upon market settlement counts as disposal proceeds

Applying CGT treatment, traders generating annual gains under £3,000 incur zero tax. Higher-volume traders must declare positions via Self Assessment under the Cryptoassets section.

Treatment 3: Income Tax (Trading Income)

Should HMRC determine your Polymarket participation constitutes a trade, all winnings become taxable income subject to Income Tax:

• Tax rates: 20% (basic), 40% (higher), 45% (additional)
• Self-employed National Insurance contributions may be payable
• Trading losses from unprofitable years may be applied against future trading profits
• Likely applies where: activity is regular and methodical, consumes considerable time, represents a principal or ancillary income stream

HMRC's Published Guidance on Cryptoassets

HMRC released its Cryptoassets Manual (CRYPTO) in 2022 with revisions published in 2024. Relevant provisions affecting Polymarket participants include:

• USDC, as a stablecoin, qualifies as a cryptoasset — all disposals incur CGT
• Converting crypto to purchase market contracts or tokens may constitute a taxable disposal of USDC
• HMRC has not established a dedicated classification for prediction market instruments
• From 2025 onwards, cryptoasset reporting obligations require UK-regulated platforms to supply transaction data to HMRC — this creates enhanced visibility into user activity

Practical Record-Keeping for UK Polymarket Traders

Irrespective of the ultimate tax classification applied, maintain the following documentation:

1. Deposit records: transaction date, sterling amount deposited, USDC received, conversion rate applied
2. Position details: opening date, USDC committed, resolution date, USDC settlement amount
3. Withdrawal records: transaction date, USDC withdrawn, sterling equivalent received, conversion rate
4. Year-end reconciliation: cumulative USDC inflows, cumulative USDC outflows, net sterling gain or loss

Platforms including Koinly and CoinTracker facilitate Polymarket/Polygon transaction tracking and produce HMRC-compliant CGT calculations without manual effort.

The Gambling Tax-Free Argument in Practice

Certain UK Polymarket traders contend their returns constitute gambling winnings and therefore escape taxation, citing parallels with Betfair Exchange (which enjoys clear tax-free status). This reasoning possesses theoretical strength but encounters substantial practical barriers:

1. Polymarket operates without UKGC authorisation — HMRC has not confirmed whether the gambling exemption encompasses unregulated overseas platforms
2. The cryptographic nature of settlement means HMRC typically views transactions as cryptoasset disposals rather than gambling events

Absent explicit HMRC clarification, the prudent course involves reporting under CGT principles whilst documenting the gambling-exemption argument as an alternative legal position.

Reporting Polymarket Winnings on Self Assessment

Where reporting obligations arise (gains exceeding £3,000 or income surpassing £1,000):

1. File Self Assessment SA100 (or utilise HMRC's online Personal Tax Account portal)
2. For CGT scenarios: complete SA108 — record cryptoasset disposals under "Other property, assets and gains"
3. For trading income scenarios: complete SA103 (self-employed) or SA800 (partnership)
4. Submission deadline: 31 January following the relevant tax year

FAQ — Polymarket Tax UK

Do I need to tell HMRC about small Polymarket winnings?

Where aggregate capital gains from all sources (encompassing USDC transactions) remain beneath £3,000 during 2026/27, reporting is unnecessary. Basic rate taxpayers with gains under £3,000 face no tax liability and no disclosure requirement.

Are losses on Polymarket tax-deductible?

Under CGT treatment, losses qualify for offset against capital gains in the current or subsequent tax years. Under trading income treatment, losses similarly reduce other trading profits. Document all unsuccessful positions comprehensively.

Does HMRC know about my Polymarket activity?

From 2025, cryptoasset reporting obligations require UK-regulated exchanges (Coinbase UK, Kraken) to furnish HMRC with user transaction data exceeding £1,000 annually. Prediction market activity identifiable through such reports may prompt HMRC investigation of non-compliant traders.

Start trading on PolyGram →