base fee

The base fee is the per-gas price that every transaction in a block must pay, set by the protocol itself rather than bid by users. Recorded in each block header as baseFeePerGas, it is the floor below which no transaction can be included, and uniquely it is burned — destroyed and removed from circulation rather than paid to anyone. It is the centerpiece of the EIP-1559 fee market.

Its value moves by a simple, deterministic rule that reacts to congestion. Each block has a gas target (half the block gas limit). If the parent block used exactly the target, the base fee stays flat. If the parent was fuller than target, the base fee for the next block increases proportionally to how much it overshot, capped at +12.5% per block; if emptier, it decreases by up to 12.5%. The exact formula nudges the fee by (gas_used − gas_target) / gas_target, scaled by 1/8. Because the change per block is bounded, the base fee cannot spike instantly — but a sustained burst of demand can compound it upward over a handful of blocks, and a lull brings it back down just as mechanically.

This self-adjusting design is what makes Ethereum fees estimable. A wallet can read the current base fee, see it can move at most 12.5% in the next block, and confidently set a maxFeePerGas that covers a few blocks of possible increase — so a transaction stays valid through normal volatility instead of getting stuck the way fixed gas-price bids used to.

Burning the base fee has two effects worth separating. Economically, it links ETH supply to usage: when the network is busy, ETH is burned faster than it is issued to validators, making net supply deflationary during high demand. Game-theoretically, burning rather than paying the proposer removes the incentive for proposers to artificially inflate fullness to harvest fees — the proposer earns only the separate priority tip.