Mempool Minimum Fee

Overview

A node’s mempool minimum fee can rise when its configured memory capacity is full. Lower-fee transactions are evicted, and new transactions below the rolling threshold are rejected until demand falls and the threshold decays. This value differs from a protocol-mandated minimum relay fee and from the fee likely needed for prompt block inclusion. Nodes can report different thresholds because their mempool contents, limits, peers, and configuration vary.

Wallets should combine node policy data with recent block and mempool fee distributions when estimating fees. A transaction above one node’s minimum may still propagate poorly or wait indefinitely. Operators should monitor threshold changes and communicate specific rejection reasons rather than presenting every low-fee failure as consensus invalidity. An estimate should identify the fee unit, network, block context, and transaction parameters used to calculate it. Wallet defaults, quoted caps, and minimum protocol charges are different values, so interfaces should label each field and avoid presenting a maximum authorization as the amount ultimately paid.

Calculations should use integer base units and preserve the original fields submitted by the signer, because rounded display values are insufficient for reconciliation or incident review. Operational handling of Mempool Minimum Fee should account for congestion, replacement rules, rejected fee settings, and software-version differences.

Integrations should store the canonical transaction identifier, inclusion block, execution result, consumed resources, and effective fee reported by the final receipt. A pending quote can change before inclusion, and a transaction that fails at execution may still consume a network fee. Technical takeaway: Mempool minimum fee is a dynamic local retention threshold, not a universal network price or guarantee of timely confirmation.