What is the 'estimated fee'?

On the Ethereum network, the size of fees depends on a number of factors, including, for instance, network load and the complexity of a transaction. Therefore, it is impossible to precisely say what a transaction fee will be before the transaction has actually occurred. Nevertheless, you can see the more accurate value of the gas fee in the confirmation window right before the swap. An estimated fee is provided on the 1inch user interface merely to give users some guidance.