Why swapping the full native-coin balance can fail

Swapping every unit of the native coin can leave nothing to pay the transaction fee. The spendable input is usually lower than the displayed native balance when you pay gas from that same account.

Why Max is an estimate

A wallet or aggregator may reserve an estimated fee when you choose Max. That estimate can change with the route and network conditions. Ethereum transaction fields separate the transferred value from the gas budget and fee parameters, so both must fit the account’s funding requirements.

Do not reuse a Max amount calculated for a different route, an earlier fee estimate or a simple transfer. The swap may call several contracts, making its execution budget different.

Adjust the input, then review the quote again

1. Confirm you are spending the chain’s native coin rather than a wrapped token.
2. Refresh the route and wallet fee estimate.
3. Reduce the input enough to cover the displayed maximum execution cost and your intended remaining balance.
4. Review the changed output and minimum received before signing.

There is no universal reserve amount that fits every chain and transaction. A fixed suggestion can become inadequate during congestion or wastefully large for a simpler operation.

Also plan for what comes next. Even after this swap succeeds, moving the acquired tokens or changing an approval may require another native-fee payment. Keeping a usable balance is an operational choice, not an extra aggregator charge. If the wallet explicitly supports a different fee-paying mechanism, assess its quoted cost and conditions separately.