Polymarket Tax UK: HMRC Guide to Prediction Market Winnings 2026

Among British traders using Polymarket, questions about tax obligations rank among the most pressing. This guide examines the current HMRC position on Polymarket tax UK throughout 2026, drawing on official HMRC guidance regarding cryptoassets and gambling winnings.

Three Possible Tax Treatments

HMRC has not released dedicated guidance on prediction market contracts. Drawing from established HMRC rules governing cryptoassets and gambling, three tax treatments are conceivable:

Treatment 1: Gambling Winnings (Tax-Free)

Should HMRC categorise your Polymarket participation as gambling, winnings would be exempt from UK tax under established gambling exemptions. This represents the most advantageous scenario and may apply where:

• Your trading occurs infrequently and lacks systematic structure
• You do not rely on it as a main or auxiliary income stream
• Your conduct aligns more with consumer gambling than investment behaviour

Conventional UKGC-regulated betting platforms (Betfair, Smarkets) unquestionably qualify as tax-exempt gambling. Polymarket operates via crypto and falls outside the Gambling Act framework — HMRC may decline to apply the same exemption without explicit confirmation.

Treatment 2: Capital Gains Tax (CGT)

HMRC's Cryptoassets Manual treats most cryptoasset transfers as taxable capital events subject to CGT. Under this framework:

• Each profitable trade constitutes a USDC disposal resulting in a gain
• CGT rates: 18% (standard-rate payer) or 24% (higher/additional-rate payer) since April 2024
• Annual exemption: £3,000 (2026/27) — gains beneath this threshold incur no tax
• Losses may be deducted from gains
• USDC obtained upon settlement represents disposal proceeds

Applying CGT treatment, modest traders whose annual gains stay below £3,000 face no tax bill. Larger-scale traders would declare transactions via Self Assessment under the Cryptoassets section.

Treatment 3: Income Tax (Trading Income)

Should HMRC determine your Polymarket engagement constitutes a trade, winnings would be income taxed under Income Tax rules:

• Tax rates: 20% (standard), 40% (higher), 45% (additional)
• Self-employment National Insurance contributions may apply
• Trading losses in any year may be carried forward to offset future trading profits
• Probable if: activity is regular, time-intensive, constitutes a main or secondary income source

HMRC's Published Guidance on Cryptoassets

HMRC released its Cryptoassets Manual (CRYPTO) in 2022 with updates in 2024. Relevant points for Polymarket users include:

• USDC, as a stablecoin, qualifies as a cryptoasset — CGT applies when disposed of
• Exchanging crypto to acquire tokens or contracts may trigger a taxable event (USDC disposal)
• HMRC presently lacks a dedicated framework for prediction market contracts
• From 2025, UK-regulated exchanges must furnish HMRC with user transaction data — HMRC is assembling comprehensive transaction intelligence

Practical Record-Keeping for UK Polymarket Traders

Whichever tax treatment ultimately governs your position, preserve the following documentation:

1. Each deposit date: sterling amount transferred, USDC received, applicable exchange rate
2. Every market position: opening date, USDC committed, settlement date, USDC returned
3. Each withdrawal date: USDC quantity withdrawn, sterling received, exchange platform used
4. Year-end reconciliation: cumulative USDC deposited, cumulative USDC withdrawn, net sterling gain or loss

Koinly and CoinTracker both accommodate Polymarket/Polygon transaction data and produce HMRC-compatible CGT computations without manual intervention.

The Gambling Tax-Free Argument in Practice

Certain UK Polymarket participants contend their winnings qualify as gambling winnings exempt from tax, making a parallel to Betfair Exchange (manifestly tax-exempt). This reasoning carries weight for occasional traders yet encounters two significant hurdles:

1. Polymarket lacks UKGC licensing — HMRC has not confirmed whether the gambling exemption covers unlicensed international platforms
2. The blockchain-based character of transactions causes HMRC to perceive them as cryptoasset transfers, not gambling bets

Absent explicit HMRC direction, the prudent course involves reporting under CGT whilst appending commentary outlining the gambling-exemption rationale as a supplementary position.

Reporting Polymarket Winnings on Self Assessment

Should you be obliged to file (gains exceeding £3,000 or income surpassing £1,000):

1. Submit Self Assessment SA100 (or file electronically via HMRC Personal Tax Account)
2. For CGT: complete SA108 — record cryptoasset disposals under "Other property, assets and gains"
3. For trading income: complete SA103 (sole trader) or SA800 (partnership)
4. File by 31 January after the tax year concludes

FAQ — Polymarket Tax UK

Do I need to tell HMRC about small Polymarket winnings?

Provided your aggregate capital gains across all sources (encompassing USDC transactions) fall beneath £3,000 in 2026/27, declaration is unnecessary. If you fall within the basic-rate band with gains under £3,000, no tax liability arises and filing is not required.

Are losses on Polymarket tax-deductible?

Under CGT treatment, absolutely — losses offset capital gains within the same or subsequent tax years. Under trading income treatment, losses similarly reduce other trading profits. Maintain documentation of all unprofitable positions.

Does HMRC know about my Polymarket activity?

From 2025 onwards, UK-regulated exchanges (Coinbase UK, Kraken) automatically furnish HMRC with user transaction particulars exceeding £1,000 annually. Transactions identifiable as prediction market dealings may prompt HMRC investigations if not voluntarily disclosed.

Start trading on PolyGram →