Max Fee Per Gas

Overview

The maxFeePerGas field is part of EIP-1559-style transactions. It protects the sender from paying more than a chosen total price for each unit of gas. The cap covers both the protocol base fee and the proposer priority fee, rather than representing a separate additional charge.

At execution, the effective gas price is generally the current base fee plus the effective priority fee, bounded by maxFeePerGas. Any unused difference between the cap and the effective price is not charged. The total fee still depends on actual gas used, so a high cap does not by itself determine total transaction cost.

A transaction becomes ineligible for inclusion when the current base fee exceeds its max fee per gas. Wallets may replace the transaction with a higher fee cap, subject to nonce and replacement rules. A cap chosen with headroom can tolerate several base-fee increases without requiring immediate replacement.

Payment applications should store the submitted cap, the base fee of the inclusion block, the effective gas price from the receipt, actual gas used, and replacement history. This supports accurate reconciliation and explains why a user’s maximum authorization can differ from the amount finally charged.

Max fee per gas differs from max priority fee per gas. The first limits the combined base fee and tip; the second limits only the proposer tip. Legacy gasPrice transactions use a single price field and should not be interpreted through the same field structure.

For example, if a transaction sets maxFeePerGas well above the current base fee, the sender does not automatically pay the entire cap. The effective price depends on the included block’s base fee and the allowed priority fee. Payment systems should preserve the cap, base fee, effective gas price, and gas used so treasury teams can explain the actual charge and distinguish it from the wallet’s worst-case authorization.