How to track cost basis for a Mantle bridge swap

Track a Mantle bridge swap by recording what left your wallet, what arrived, and the value and fees at each step. A bridge moves tokens between networks; a swap trades one token for another. Some journeys do both, so keep the transfer and trade as separate records. This makes it easier to explain how you reached the final amount and its cost basis, the value used to track a token for tax or accounting.

What records should you keep for each swap?

Keep the transaction details for both the sending and receiving sides, plus the swap itself if it is a separate transaction. A transaction hash is the public identifier for an on-chain action. Save it with the date and time, wallet address, network, token, amount, and any fee shown in the transaction. Export or save the wallet and exchange records too; a block explorer can help check a transaction, but it may not show every detail you need.

If you are new to the transfer steps, this mantle bridge guide covers when a bridge fits. For your records, note whether the same token simply moved across networks or whether you traded it for another token. That distinction can change how the event is treated in your accounting.

How do you work out the cost basis?

Start with the tokens you acquired and the value you paid for them, using the method and currency required for your records. If you bridge the same token to Mantle, record the outgoing amount and the amount received, including any difference caused by fees. Many accounting approaches carry the original basis across a same-token transfer, but rules vary by jurisdiction.

If the route includes a swap, record the value of the tokens given up and received at that time, along with the fee. For example, if a wallet sends one token, pays a fee, then receives a different token, the outgoing trade and incoming acquisition need their own entries. Do not treat the final wallet balance alone as the full history.

How can you reconcile a route with several steps?

Use one row per on-chain action, in time order. This makes the route easier to check when a bridge transfer and a swap happen in separate transactions.

• Match the sending transaction to the receiving transaction by token, amount, and timing.
• Record bridge fees and swap fees separately, with the token each fee was paid in.
• Keep a note for any amount difference, such as a fee or a token conversion.
• Check that the ending token balance matches the recorded receipts and later transfers.

What should you do when the records do not match?

Pause the reconciliation and find the missing step before assigning a basis to the final tokens. Check the wallet history and transaction details on both networks, then compare token amounts and fee units. A displayed dollar value may use a different price source or time than your accounting method, so preserve the underlying amounts and timestamps as well.

The practical rule is simple: preserve the path, not just the destination. Clear records of each transfer, swap, and fee make later reporting easier and help you explain how the final cost basis was reached. Tax treatment differs by location, so use the records with the rules that apply where you file.