EIP‑1559 fee calculation ambiguity in web3.eth.getGasPrice for low‑traffic workloads

Direct answer

Replace web3.eth.getGasPrice with a custom calculation that uses the latest block’s baseFeePerGas plus a chosen priority fee (with a small buffer). This yields the correct maxFeePerGas and maxPriorityFeePerGas parameters for EIP‑1559 chains and avoids the over‑payment observed with the legacy gasPrice field.

Confirmed facts

• As of web3.js v1.x (the current stable release) there is no built‑in helper that directly computes maxFeePerGas and maxPriorityFeePerGas.
• The correct EIP‑1559 transaction fields are maxFeePerGas and maxPriorityFeePerGas; maxFeePerGas should be set to baseFeePerGas + priorityFee (optionally plus a 10‑20 % buffer to absorb short‑term base‑fee swings).
• web3.eth.getGasPrice returns the legacy gasPrice field, which on EIP‑1559 chains reflects the miner tip and can exceed baseFeePerGas + modest priority fee when traffic is low.

Likely explanation

The library’s getGasPrice method was designed for pre‑EIP‑1559 chains and simply returns the gasPrice value from the latest block. On EIP‑1559 networks that value is not the total fee a user will pay; it only represents the priority (tip) component. Consequently, when the base fee is low (e.g., during off‑peak periods) the returned legacy price can be substantially higher than the sum of base fee + tip, leading to overpayment and unpredictable cost budgeting for low‑traffic services.

Steps needed for this case

1. Fetch the latest block: const block = await web3.eth.getBlock('latest');
2. Extract baseFeePerGas from the block (in wei).
3. Choose a priority fee (e.g., 1 gwei = 1 000 000 000 wei) that reflects the desired tip for miners.
4. Add a small buffer (optional, e.g., 15 % of baseFeePerGas) to protect against rapid base‑fee increases between the block query and transaction submission.
5. Compute:
• maxPriorityFeePerGas = priorityFee
• maxFeePerGas = baseFeePerGas + priorityFee + buffer
6. Submit the transaction with maxFeePerGas and maxPriorityFeePerGas fields (instead of gasPrice).

Missing diagnostic detail

If you need to fine‑tune the buffer size, please specify the acceptable over‑payment threshold (e.g., “no more than 10 % above baseFee + tip”) so the buffer can be calibrated accordingly.