Arbitrum (ARB) Tax UK: Layer 2 Activity, Airdrops and Gas
How UK Capital Gains Tax applies to Arbitrum — the ARB airdrop as income, swaps and bridging on the L2, low gas fees, and the records HMRC expects for 2025/26.
Arbitrum is one of the busiest Ethereum Layer 2 networks, and its cheap transactions encourage a lot of swapping, bridging and DeFi activity. For UK users that volume of on-chain action translates into more taxable events than people expect, plus a specific question about the original ARB airdrop.
The ARB airdrop is income
If you claimed ARB in the token airdrop, HMRC's treatment depends on the circumstances. Where an airdrop is received in return for doing something — past usage, qualifying activity, or anything that looks like a service — it is taxed as income at the GBP value on the day you received it. Many users treat the ARB drop this way. That value then becomes the cost basis for the tokens.
Swaps and disposals on Arbitrum
Every time you swap one token for another on an Arbitrum DEX — ETH for ARB, USDC for ETH, or any pairing — you make a disposal of the token you gave up. The fact that fees are tiny doesn't reduce the number of taxable events; it tends to increase them, because cheap gas encourages frequent trading. Each swap needs a GBP gain or loss calculated against your Section 104 pool.
Does bridging trigger tax?
Bridging ETH from Ethereum mainnet to Arbitrum is generally not a disposal, because you still hold the same asset — you've moved it, not sold it. However, if a bridge issues you a different, wrapped representation of the asset, the position is less clear and may be a disposal. Keep records of every bridge transaction so the treatment can be reviewed.
Gas fees and your cost basis
Gas paid in ETH to execute an Arbitrum transaction is an allowable cost. For an acquisition it adds to your cost basis; for a disposal it reduces your proceeds. Arbitrum fees are small, but across hundreds of transactions they add up and shouldn't be ignored. You can monitor live Arbitrum versus mainnet costs on the CryptoLens gas tracker.
Rates and reporting
Net gains above the £3,000 annual allowance are taxed at 18% or 24% for 2025/26. High transaction counts on L2s are exactly where manual tracking breaks down. CryptoLens reads your Arbitrum address, applies pooling, and consolidates it with your other chains into one HMRC figure.
This is general information rather than personal tax advice.
Frequently asked questions
Is the Arbitrum (ARB) airdrop taxable in the UK?
Usually yes. Where an airdrop is received in connection with activity or past usage, HMRC treats it as income at its GBP value on receipt, and that value becomes your cost basis for any later sale.
Do I pay tax for bridging assets to Arbitrum?
Generally no, if you still hold the same asset after bridging — that's a transfer, not a disposal. It's less clear if you receive a different wrapped token, so keep records of every bridge.
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