When is Ethereum gas fee calculated during execution of contract. I was wondering if i take out flash loan and if the trade happened to be profitable, will the profit be able to offset transaction fee or I would have to pay upfront?

1 Answer 1


When you create a transaction you set two parameters:

  • gas: Maximum amount of gas to be used
  • gasPrice: Price to pay for each gas unit

To execute the transaction your account needs to have at least gas * gasPrice ether.

Before executing your account is charged with gas * gasPrice.

After the transaction has completed its execution unused gas and refunded gas are returned to your account.

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