How Polymarket Works - What HMRC Sees on the Blockchain
Polymarket is a decentralised prediction market platform. You buy binary outcome contracts - "Yes" or "No" shares - settled in USDC on the Polygon blockchain. When a market resolves, winning shares are redeemed at $1 each and losing shares expire worthless. You can also sell your shares before settlement at the current market price.
Polymarket does not issue any tax documents equivalent to a UK broker statement or tax certificate. Your allowable cost is established when you purchase shares; your proceeds are determined on settlement or sale. All trading runs through a proxy wallet - a smart contract address distinct from your sign-in wallet - so your trading wallet address is the starting point for any tax calculation.
The Two UK Tax Layers for Polymarket Users
HMRC has not published any guidance chapter specifically addressing prediction markets. The safest approach for UK users is a split analysis, treating the crypto funding leg separately from the event-position outcome.
Layer 1 - Crypto funding disposals
When you buy USDC with GBP and later sell it back to GBP, you trigger a chargeable disposal under CGT rules. Section 104 pooling applies to USDC; same-day and 30-day matching rules are applied before the pool is used. If USDC held its peg closely, the gain may be very small - but it is calculable and reportable if your total CGT position requires it.
If you funded your account by swapping another cryptoasset into USDC - for example, ETH to USDC - that swap is itself a chargeable disposal of the ETH under the normal UK disposal rules. Each step in the funding chain is assessed separately. This layer applies regardless of how the event-position outcome is ultimately classified.
Layer 2 - Event-position P/L (review-required)
The profit or loss on your Polymarket positions is where the analysis becomes fact-sensitive. Three possible UK treatments apply:
- Gambling or exempt - if your activity is characterised as a wagering contract, HMRC's betting manuals indicate that profits are ordinarily outside Income Tax and CGT. Losses are not relievable. Having expertise or a systematic approach does not by itself make a punter taxable as a trader under HMRC's betting guidance.
- Capital gains - if the position contracts are treated as capital assets, gains and losses fall within CGT at 18% or 24% depending on your total income, with the £3,000 Annual Exempt Amount applied.
- Trading income - only if the activity is organised, systematic and profit-seeking in a business-like way would HMRC treat it as a trade. Profits would then be taxable at your marginal Income Tax rate. This applies in unusual cases and is far less common for ordinary retail participants.
No direct HMRC ruling or published chapter has addressed prediction markets specifically in the reviewed material. The correct classification depends on your own facts and is best reviewed with a qualified UK tax adviser.
Gambling Commission Position - 4 February 2026
On 4 February 2026, the Gambling Commission published its view that current prediction-market products offered in Great Britain appear to fall within UK gambling law as betting-intermediary or betting-exchange style products. The Commission also noted that operators not licensed to offer gambling in Great Britain should not be targeting or transacting with consumers there.
This is a regulatory position under the Gambling Act 2005, not a tax ruling from HMRC. Gambling regulation and tax treatment are handled by different bodies under different legal frameworks. The Commission's position may be relevant context when characterising the nature of your activity, but it does not determine your tax liability directly.
The Crypto Funding Layer - CGT Applies Even If Profits Are Exempt
This point is often missed. Even if your event-position outcome is classified as gambling and exempt, the USDC or other cryptoassets you used are still subject to CGT rules on disposal.
- Buying USDC with GBP: acquisition at your GBP allowable cost, entering the Section 104 pool
- Transferring USDC to your Polymarket proxy wallet: a transfer between addresses you control - not a disposal, as beneficial ownership remains with you
- Withdrawing USDC back to your wallet: same - not a disposal
- Selling USDC back to GBP: chargeable disposal - gain or loss equals sterling proceeds minus Section 104 pool cost
If you originally acquired USDC by swapping from ETH, BTC or another cryptoasset, each of those swaps was itself a chargeable disposal of the original token. The Section 104 pool for each token type is maintained separately. Even a fraction of a penny per USDC in gain or loss is technically reportable when aggregated across all disposal events.
What DYOR.tax Calculates for UK Polymarket Traders
- Proxy wallet scan covering all trades, settlements and redemptions
- Crypto funding disposals calculated under Section 104 pooling with same-day and 30-day matching
- Event-position P/L shown as review-required with relevant classification frameworks set out
- Annual Exempt Amount tracked (£3,000 for 2025-26 and 2026-27)
- SA108 capital gains filing guidance for your Self Assessment return
- Optional History CSV enrichment for deposits and withdrawals
UK Filing Requirements for Polymarket Users
- Event-position P/L (if gambling-exempt): ordinarily not reportable to HMRC
- Event-position P/L (if CGT): report on SA108 (Capital Gains Summary) within Self Assessment if total gains exceed the £3,000 Annual Exempt Amount; those already registered for Self Assessment must also report if total disposal proceeds in the year exceed £50,000, even if gains are within the Annual Exempt Amount
- Event-position P/L (if trading income): report on SA100 and SA103F (Self-Employment pages)
- Crypto funding disposals: report on SA108 if gains or proceeds exceed the relevant thresholds, regardless of how the event-position outcome is classified
- 2025-26 deadlines: notify HMRC by 5 October 2026 if you need to register for Self Assessment; file online and pay by 31 January 2027
- UK CARF: from 1 January 2026, UK cryptoasset service providers are required to collect user data under the Reporting Cryptoasset Service Providers Regulations 2025; the first reporting window runs from 1 January 2027 to 31 May 2027, covering calendar year 2026
- Records: keep records of every disposal for at least 5 years after the Self Assessment filing deadline
Common Polymarket Tax Mistakes in the UK
- Assuming all activity is tax-free because gambling is exempt: The crypto funding leg is still a separate CGT event even if prediction market profits are ultimately exempt. The two layers must be analysed separately.
- Forgetting that crypto-to-crypto swaps on the way to USDC create disposal events: Every swap of ETH, BTC or another token into USDC is a chargeable disposal under UK rules, regardless of your Polymarket outcome.
- Not registering for Self Assessment: CGT on crypto funding disposals still requires a Self Assessment return if gains exceed the threshold. Failing to notify HMRC by 5 October following the end of the tax year carries its own penalties.
- Assuming high-frequency activity remains gambling-exempt: HMRC may apply its badges-of-trade test. Systematic, organised, profit-seeking activity could be reclassified as a trade, removing the gambling exemption entirely.
Related Resources
For broader UK crypto tax context, the UK crypto tax calculator covers Section 104 pooling, the £3,000 Annual Exempt Amount, and SA108 reporting. The Polymarket and Kalshi tax guide examines the gambling exemption analysis in more detail, and the UK crypto tax deadline page has the key Self Assessment dates for 2025-26.
For Polymarket traders in other countries: USA - Canada - Australia - New Zealand - India - South Africa
Back to the Polymarket tax calculator main page.