maxFeePerGas

maxFeePerGas is a parameter used in Ethereum transactions following the London hard fork (EIP-1559). It specifies the maximum total price a sender is willing to pay per unit of gas for that transaction, including both the base fee and the tip to the miner. Alongside maxPriorityFeePerGas (the maximum priority fee per gas the sender is willing to pay), maxFeePerGas governs how expensive a transaction can become during network congestion.

How it works: each block has a baseFeePerGas, which is burned as part of EIP-1559. The actual fee paid per gas to miners is the baseFeePerGas plus an actual priority fee. The actual priority fee per gas is the minimum of maxPriorityFeePerGas and (maxFeePerGas − baseFeePerGas). If baseFeePerGas already exceeds maxFeePerGas, the transaction cannot be included.

Impact and purpose: maxFeePerGas provides a ceiling on expected costs for users, improving fee predictability compared with the previous system. It also helps miners by signaling potential revenue through the priority fees. The base fee being burned aims to adjust monetary issuance and reduce supply over time.

Practical examples: if baseFeePerGas is 20 gwei, maxFeePerGas is 60 gwei, and maxPriorityFeePerGas is 15 gwei, the actual priority fee would be min(15, 60−20 = 40) = 15 gwei, so the total price per gas is 35 gwei. If maxPriorityFeePerGas is 40 gwei, the actual priority fee would be min(40, 40) = 40 gwei, for a total of 60 gwei.

Background: introduced with EIP-1559 as part of the London upgrade to reform Ethereum’s fee market and improve fee stability.