How the base fee moves
Each block has a gas target equal to half of its gas limit. When a block uses more gas than the target, the next block's base fee goes up; when it uses less, it goes down. The maximum step is 12.5% per block, reached when a block is completely full. Six full blocks in a row raise the base fee by a factor of 1.125โถ โ 2.03 โ that is where the common wallet rule of thumb "max fee = 2 ร base fee + tip" comes from: it keeps the transaction valid through roughly six full blocks, about 72 seconds.
The base fee is burned. The tip goes to the validator who includes the transaction, and in normal conditions a small tip is enough because blocks are rarely full for long.
worst base fee = current base fee ร 1.125 ^ full blocks
maxFeePerGas = worst base fee + tip
paid per gas = min(maxFeePerGas, base fee of your block + tip)
cost = gas used ร paid per gas รท 10โน ETHChoosing the numbers
- Take the current base fee from your wallet or a block explorer; it is shown in gwei for the latest block.
- A tip of 0.1โ2 gwei is typical on Ethereum mainnet when the network is quiet. Raise it only if you need the next block and blocks are full.
- "Blocks to survive" is a safety margin. More blocks means a higher cap, not a higher bill โ the unused part stays in your wallet.
- Gas used depends on what you do: 21,000 for a plain ETH transfer, around 45,000โ65,000 for an ERC-20 transfer, more for swaps and mints.
If the base fee rises above your max fee, the transaction is not rejected โ it waits in the mempool until the base fee falls back, or until you replace it with a higher max fee and the same nonce.
Worked example
Base fee 2 gwei, tip 0.5 gwei, six full blocks of margin. The worst-case base fee is 2 ร 2.03 = 4.05 gwei, so maxFeePerGas = 4.55 gwei. If your transaction lands in the next block at a 2 gwei base fee you pay 2.5 gwei per gas: an ETH transfer costs 21,000 ร 2.5 รท 10โน = 0.0000525 ETH. The cap you approved was 0.0000956 ETH; the difference was never charged.
Layer 2 networks
Arbitrum, Base and Optimism use the same transaction format, but their total fee also includes a charge for posting data to Ethereum. The execution part follows the same base fee and tip logic; the data part is set by the rollup. Use this calculator for the execution part and your wallet's estimate for the total.
Frequently asked questions
+What should I set as maxFeePerGas?
A common safe choice is 2 ร current base fee + tip. It covers about six consecutive full blocks. You only pay the base fee of the block that includes you plus the tip.
+Do I lose the difference between max fee and the actual fee?
No. The unused part is never deducted from your balance. Your wallet only needs enough ETH to cover gas limit ร max fee at signing time.
+Why is my transaction pending if the max fee is high enough?
Most often the tip is too low compared with other transactions, or an earlier transaction from the same address (lower nonce) is still pending and blocks it.
+How much can the base fee rise in one block?
At most 12.5%, and only when the previous block was completely full. It falls by up to 12.5% when a block is empty.
+Is the base fee the same on every EVM chain?
No. Each chain has its own base fee and parameters. BNB Smart Chain and Polygon have their own fee rules, and layer 2 rollups add a data fee.
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