Why the final network fee differs from the estimate

A network-fee estimate forecasts work and the price of that work. A receipt reports the included transaction. The two can differ because execution consumes a different amount of gas, the effective gas price differs from the estimate, or the original display used a maximum spending allowance.

Compare both factors

Assume an estimate used 200,000 gas at 3 gwei: 0.0006 ETH. The hypothetical included transaction uses 175,000 gas at 2.8 gwei: 0.00049 ETH. Its fee is 0.00011 ETH below the estimate.

The lower result does not establish that the route became more efficient. Some of the difference came from gas usage and some from price per gas. Preserve both fields before attributing the saving.

EIP-1559 specifies how an Ethereum transaction's fee caps interact with the included block's fee and priority payment. A cap is not an instruction to charge the entire maximum.

Match the same transaction boundary

Check whether the estimate covered the swap alone or also a separate approval. Comparing one swap receipt with a combined setup-and-swap estimate creates a false discrepancy. Likewise, do not compare gas units from a receipt with a fiat value that includes additional service charges.

If a wallet shows a dollar estimate and the receipt shows a dollar total, native-token price changes can contribute to the difference. Reconcile in the native asset first, then compare valuations.

When investigation is warranted

A small estimate gap is not inherently suspicious. A large gap deserves an explanation of the submitted operations, the consumed units and the price applied. If the final route differed from the preview, the computational workload may also differ.

Keep the quote, transaction hash, receipt and displayed estimate together. Those records distinguish a forecasting error from an omitted transaction or a change in the user's actual request.