Ethereum Priority Fees: Get Token Swaps Included Promptly
An Ethereum priority fee is the per-gas tip a transaction offers a validator for inclusion. It matters most when blocks are crowded: a higher tip can improve a swap’s position among eligible transactions, but it cannot make an underfunded fee cap valid or guarantee a particular block.
What does the priority fee buy?
A type-2 Ethereum transaction sets both maxPriorityFeePerGas and maxFeePerGas. The base fee is set by the protocol and burned; the priority fee goes to the block’s validator. The amount actually paid per gas is the base fee plus the effective tip, which is capped by maxFeePerGas minus the base fee.
This is an incentive, not a reservation. Validators and block builders choose transactions under block-space constraints, and ordering can reflect more than the visible tip, including private order flow and value available from transaction execution. For someone using Fermi swap, the practical question is whether the wallet’s suggested tip matches the urgency of this particular token exchange.
When blocks are quiet, a tip of a few gwei may be enough; during contention, recent inclusion estimates matter more than any fixed “normal” value. Ethereum.org’s gas documentation explains that the tip signals urgency, while EIP-1559 defines the fee cap and the rule that limits the effective tip.
How do fee caps affect inclusion?
A transaction is eligible only if its maxFeePerGas is at least the base fee of the block that might include it. If the base fee rises above that cap while the transaction waits, the transaction becomes temporarily ineligible, regardless of its priority fee. The cap therefore buys room for base-fee movement; it does not promise to pay the full cap.
The base fee adjusts from one block to the next according to the previous block’s gas use. At maximum block usage, it can rise by up to 12.5% in one block. As an illustrative example, if the current base fee is 20 gwei, a 50 gwei max fee leaves room for several full blocks of increases, while a 25 gwei cap leaves little headroom. A common wallet heuristic is to set the cap around twice the current base fee, plus the desired tip; check the wallet’s estimate rather than treating that heuristic as a guarantee.
Consider two illustrative swaps, each using 180,000 gas, with a 20 gwei base fee and 50 gwei max fee. One offers a 1 gwei tip; the other offers 3 gwei. Both are eligible, but when builders must choose between competing transactions, the second offers more per gas. If included at those rates, its fee is 0.00414 ETH versus 0.00378 ETH, a 0.00036 ETH difference. Actual gas used can differ from the estimate.
When is a higher tip worth it?
Raise the tip when prompt inclusion matters and current estimates show competing transactions paying more. For a routine swap with no deadline, a lower tip may be a reasonable trade-off if you can tolerate waiting; for a time-sensitive price, paying more can reduce delay, though the quote or market price may still change before execution.
If a transaction is pending, a replacement generally uses the same account nonce and must raise its fee fields enough to satisfy the node’s replacement policy; simply sending another transaction may leave both competing for that nonce. A swap that is included but reverts still consumes gas, so check that the quoted trade remains acceptable before signing. The question to ask yourself is: how much is prompt inclusion worth for this swap, given the current base fee and the cost of waiting?