A crypto swap resets the cost basis of both sides

A crypto swap can create a gain or loss on the asset you give up and a new cost basis for the asset you receive. That means a trade from one token into another is not just a change in portfolio mix: for tax purposes, it can close one position and open another. The exact treatment depends on your country’s rules; in the United States, the IRS treats digital assets as property, and generally measures gain or loss against the transferred asset’s adjusted basis.

What happens to cost basis when you swap crypto?

The asset you spend is measured against its basis, while the asset you receive gets a new basis based on the exchange’s value. If you bought 1 token for $400 and later traded it when it was worth $650, the starting point for calculating gain is the difference between that $650 value and its $400 adjusted basis. The token received would generally begin with a basis tied to its value in the exchange. No dollars need to pass through your hands for the swap to matter.

This two-sided accounting is why a swap needs two records: a disposal of the outgoing asset and an acquisition of the incoming one. The outgoing asset keeps its original purchase history up to the trade. The incoming asset starts a separate holding period and basis record. For a fuller comparison of routes and their mechanics, see thor swap. The route may affect which transactions appear in a wallet or exchange history, but it does not remove the need to identify what left, what arrived and when.

How do you value a swap and its fees?

Use the fair market value of the assets at the time the exchange takes place, converted into the currency required by your tax rules. In a direct token-for-token trade, the values on each side should broadly reconcile, though spreads, execution timing and market movement can produce differences. Save the timestamp, quantities, token identifiers, transaction hash, quoted or executed prices, and the source used to value the trade.

Fees need separate attention because “fee” can mean different things. A platform may charge a trading fee, a decentralized protocol may take a swap fee, and the network may charge gas for processing the transaction. In the US, IRS guidance on digital-asset exchange costs distinguishes costs allocated to disposing of the transferred asset from costs that may affect the basis of an asset acquired in a purchase. Treatment depends on the transaction and the applicable rules; don’t assume every fee simply increases the new token’s basis. Record the amount, asset used to pay it, and what service it covered, then apply the relevant local treatment consistently.

For example, if a wallet spends a small amount of a third token to pay network gas, that payment may itself need to be tracked as a disposal of that third token. The fee is not just an expense written beside the swap: the asset used to pay it may have its own basis and value at that moment.

How do you track lots across repeated swaps?

Each acquisition creates a lot: a quantity of an asset with its own acquisition date and basis. When only part of a wallet’s balance is swapped, you need a method allowed by your jurisdiction to identify which lot was disposed of. The method can change the calculated gain and holding period, so keep a consistent, contemporaneous record rather than choosing a lot after seeing the year’s price movements.

A useful transaction ledger includes:

• Outgoing token, quantity, acquisition date and assigned basis.
• Incoming token, quantity, timestamp and fair market value.
• Fees, including the token used to pay them and the transaction purpose.
• Wallet or platform, transaction identifier and valuation source.

Wallet transfers between addresses you control usually differ from swaps because ownership has not changed, but preserve the transfer record and separate any network fee. That makes it easier to distinguish a movement of existing holdings from a sale or exchange. A bridge can involve several steps and contract interactions, so reconcile the source and destination records before treating a missing token as a disposal or assuming the destination token is a continuation of the original lot.

What should you check before filing?

Reconcile every swap against wallet data, exchange statements and on-chain records, then check that each outgoing quantity has a corresponding acquisition or documented fee. Aggregators and tax software can help join records, but they may miss unsupported chains, mislabel wrapped assets, or assign inconsistent values when the trade spans multiple transactions. Review those cases against the underlying transaction details.

The practical trade-off is between simplicity and precision. A single documented valuation method and complete lot records take effort at the time of each trade, but they reduce guesswork later. A spreadsheet can work for a small number of swaps; a larger history may need software plus manual review of exceptions. Keep the source records and calculation trail, especially where a swap crossed wallets, used several tokens, or paid fees in a different asset.

The main signal to watch is not only the portfolio’s value at year-end, but whether every trade has a defensible timestamp, value and lot assignment. Rules for reporting and broker statements can change, and statements may not contain a complete basis history across self-custody wallets. Before filing, compare current local guidance with your records and check any uncertain transaction with a qualified tax professional. A swap’s new token does not erase the tax history of the one spent.