This blog post explains ex-post Ethereum gas fees transaction data, before and after the London Upgrade.
List of on-chain transaction variables used in this post,
| Variable | Description |
|---|---|
| gas | gas provided (gas limit) |
| gasPrice | paid price per gas |
| maxFeePerGas | max gas for tx |
| maxPriorityFeePerGas | max tip to miner |
| gasCost | gasUsed * gasPrice |
| gasUsed | gas used |
| type | 0: legacy, 2: EIP-1559 |
These variables can be queried from a node.
The transaction fees of legacy TransactionType 0 txes are calculated as,
total fee = gasLimit * gasPrice
Example data from a legacy tx:
"gas": 2562932,
"gasPrice": 31000000000,
"maxFeePerGas": 0,
"maxPriorityFeePerGas": 0,
"gasCost": 70459931000000000,
"gasUsed": 2272901,
"date": "2021-05-01 23:36:47 UTC",
"type": 0
The total gas fee for this transaction was,
gasCost = gasUsed * gasPrice = 70459931000000000
If look at the block on Etherscan there is no block base
fee per gas for these legacy txes and thus the “new EIP-1559 formula” cannot be applied here.
The London Upgrade (2021-08-05) introduced TransactionType 2 with new fee structure,
total fee = gasLimit * (baseFeePerGas + maxPriorityFeePerGas)
where maxPriorityFeePerGas is also called “tip”.
Example data from an EIP-1559 tx:
"gas": 226041,
"gasPrice": 114574974786,
"maxFeePerGas": 122372813094,
"maxPriorityFeePerGas": 178,
"gasCost": 16660232508657474,
"gasUsed": 145409,
"date": "2022-01-24 12:44:59 UTC",
"type": 2
The total gas fee for this transaction was,
gasCost = gasUsed * gasPrice = 16660232508657474
However, we can also calculate the total fee according to the EIP-1559 formula. The tx was mined in
block and the base fee for that block was 114574974608.
total fee = gasUsed * (baseFeePerGas + tip) = 16660232508657474
where tip = maxPriorityFeePerGas.
Thus, we can see that gasPrice = baseFeePerGas + maxPriorityFeePerGas in this example. As we
will see later, it turns out that in EIP-1559 txes gasPrice is equal to the minimum of
baseFeePerGas + maxPriorityFeePerGas and maxFeePerGas.
Let’s investigate legacy transactions, TransactionType 0, that have been sent after the London
Upgrade. Looking at an example
tx,
"gas": 51051,
"gasPrice": 97900000000,
"maxFeePerGas": 0,
"maxPriorityFeePerGas": 0,
"gasCost": 4543539000000000,
"gasUsed": 46410,
"date": "2022-01-25 00:19:55 UTC",
"type": 0
One can see that the maxFeePerGas and maxPriorityFeePerGas is zero. The transaction fee is,
gasCost = gasUsed * gasPrice = 4543539000000000
The block
base fee is 95659822298 and thus the EIP-1559 calculation would have yielded
46410*(95659822298+0) which is equal to 4439572352850180 which is lower than the actual paid
fee. Thus, this calculation cannot be used. Looking at the code below in the section
“The EIP-1559 code” we can see that actually the code sets
gasPrice = maxFeePerGas = maxPriorityFeePerGas.
Let’s look at another example tx,
"gas": 209977,
"gasPrice": 130549810158,
"maxFeePerGas": 130549810158,
"maxPriorityFeePerGas": 130549810158,
"gasCost": 17095889289620574,
"gasUsed": 130953,
"date": "2021-09-06 19:10:25 UTC",
"type": 2
Here we can see that gasPrice, maxFeePerGas and maxPriorityFeePerGas has the same value and
the tx is of TransactionType 2. The transaction fee is,
gasCost = gasUsed * gasPrice = 17095889289620574
The block base fee is 121589027525 and if we use the
EIP-1559 calculation we get 130953*(121589027525+130549810158) which is equal to
33018337211101899 and thus larger than the fee actual paid in the transaction. This cannot hold
since 33018337211101899/gasUsed = 33018337211101899/130953 = 252138837683 is larger than
maxFeePerGas which is the maximum the transaction can pay.
In this situation the maxFeePerGas is equal to 130549810158 and is the maximal amount the tx
will pay per gas. Thus, maxFeePerGas - baseFee
will go to the miner. This means that the correct calculation is,
gasCost = gasUsed * (baseFee + maxFeePerGas - baseFeePerGas) = gasUsed * maxFeePerGas
This is an interesting example and points to the fact that,
# priority fee is capped because the base fee is filled first
priority_fee_per_gas = min(transaction.max_priority_fee_per_gas,
transaction.max_fee_per_gas - block.base_fee_per_gas)
from the EIP-1559.md.
Here we can see that gasPrice = maxFeePerGas = maxPriorityFeePerGas.
The gas fee for a transaction cannot exceed maxFeePerGas. The transaction will always pay the
baseFeePerGas, and pay the maxPriorityFeePerGas, as long as the combined amount of the two fees
doesn’t exceed the transaction’s maxFeePerGas. If it does the tx will pay the maxFeePerGas and
the miner will get maxFeePerGas - baseFeePerGas.
Here is the EIP-1559 code for calculating the gas fee for EIP-1559 transactions,
# execute transactions and do gas accounting
cumulative_transaction_gas_used = 0
for unnormalized_transaction in transactions:
# Note: this validates transaction signature and chain ID which must happen before we normalize
# below since normalized transactions don't include signature or chain ID
signer_address = self.validate_and_recover_signer_address(unnormalized_transaction)
transaction = self.normalize_transaction(unnormalized_transaction, signer_address)
signer = self.account(signer_address)
signer.balance -= transaction.amount
assert signer.balance >= 0, 'invalid transaction: signer does not have enough ETH to cover attached value'
# the signer must be able to afford the transaction
assert signer.balance >= transaction.gas_limit * transaction.max_fee_per_gas
# ensure that the user was willing to at least pay the base fee
assert transaction.max_fee_per_gas >= block.base_fee_per_gas
# Prevent impossibly large numbers
assert transaction.max_fee_per_gas < 2**256
# Prevent impossibly large numbers
assert transaction.max_priority_fee_per_gas < 2**256
# The total must be the larger of the two
assert transaction.max_fee_per_gas >= transaction.max_priority_fee_per_gas
# priority fee is capped because the base fee is filled first
priority_fee_per_gas = min(transaction.max_priority_fee_per_gas, transaction.max_fee_per_gas - block.base_fee_per_gas)
# signer pays both the priority fee and the base fee
effective_gas_price = priority_fee_per_gas + block.base_fee_per_gas
signer.balance -= transaction.gas_limit * effective_gas_price
assert signer.balance >= 0, 'invalid transaction: signer does not have enough ETH to cover gas'
gas_used = self.execute_transaction(transaction, effective_gas_price)
gas_refund = transaction.gas_limit - gas_used
cumulative_transaction_gas_used += gas_used
# signer gets refunded for unused gas
signer.balance += gas_refund * effective_gas_price
# miner only receives the priority fee; note that the base fee is not given to anyone (it is burned)
self.account(block.author).balance += gas_used * priority_fee_per_gas
Useful conditions in this part of the code to understand how transaction fees are calculated are,
# The total must be the larger of the two
assert transaction.max_fee_per_gas >= transaction.max_priority_fee_per_gas
# priority fee is capped because the base fee is filled first
priority_fee_per_gas = min(transaction.max_priority_fee_per_gas, transaction.max_fee_per_gas - block.base_fee_per_gas)
# signer pays both the priority fee and the base fee
effective_gas_price = priority_fee_per_gas + block.base_fee_per_gas
According to the conditions the effective price, i.e., gasPrice, is equal to the smallest of
maxPriorityFeePerGas + baseFeePerGas and maxFeePerGas.
Similarly, here is the EIP-1559 code for calulating the gas fee of legacy transactions,
def normalize_transaction(self, transaction: Transaction, signer_address: int) -> NormalizedTransaction:
# legacy transactions
if isinstance(transaction, TransactionLegacy):
return NormalizedTransaction(
signer_address = signer_address,
signer_nonce = transaction.signer_nonce,
gas_limit = transaction.gas_limit,
max_priority_fee_per_gas = transaction.gas_price,
max_fee_per_gas = transaction.gas_price,
destination = transaction.destination,
amount = transaction.amount,
payload = transaction.payload,
access_list = [],
)
In none of the examples above is maxFeePerGas = baseFeePerGas + maxPriorityFeePerGas as you
sometimes read online.
From the EIP-1559.md: “Previous
to this change, GASPRICE represented both the ETH paid by the signer per gas for a transaction as
well as the ETH received by the miner per gas. As of this change, GASPRICE now only represents the
amount of ETH paid by the signer per gas, and the amount a miner was paid for the transaction is no
longer accessible directly in the EVM.”
On Etherscan the transaction fee is defined as “Amount paid to the miner for processing the transaction”. However, this includes the base fee that was burned.