Max Fee Per Gas

Overview

What it means and why it exists

Max fee per gas is the maximum execution-gas price, commonly set by an Ethereum sender, that the transaction is authorized to pay. It is a price ceiling per gas unit, not the final fee amount.

How it works

For an EIP-1559 transaction, the wallet sets maxFeePerGas and maxPriorityFeePerGas. At inclusion, effective price is generally the block's base fee plus the smaller of the permitted priority fee and the remaining space below maxFeePerGas. Gas used times effective price gives the execution fee. Unused price headroom is not charged.

Technical details worth understanding

If maxFeePerGas is below the prevailing base fee, a transaction cannot be included in that block. A higher cap gives flexibility across changing demand but does not guarantee fast confirmation; the priority tip and validator economics also matter. The sender must also have sufficient native token to cover the transaction's up-front balance requirement.

What can go wrong

Never compute charged fees as gas limit times max fee unless estimating a worst-case bound. Actual gas used may be lower and actual unit price may be below the cap. A contract may still revert and consume gas, and future blocks may have higher base fees.

Practical checks

A safe wallet UI labels this value as a per-unit *maximum*, not the amount the user will definitely pay. Estimate worst-case exposure as gas limit multiplied by the cap, then reconcile with actual gas used and effective price after inclusion. For a stuck transaction, verify the current base fee before recommending a replacement.

Related concepts

Ethereum, Gas Fee, Layer 2.

Further reading

Ethereum — Gas and Fees.