What is the mempool, and why should a company care?

This is a short explainer for a company that already holds bitcoin, or is about to move some. It is education, not advice, and it is not a forecast of the bitcoin price or of future fee rates.

Short answer

When a company broadcasts a bitcoin payment, the payment does not go straight into a block. It waits, with other unconfirmed transactions, in the memory pool (mempool) of each node that has accepted it. There is not one official mempool shared by the whole network: each node keeps its own list in memory, and that list is lost if the node shuts down.

Miners typically pick transactions that pay the highest fee rate, measured in satoshis per virtual byte (sat/vB). When demand for space in the next blocks is high, fee rates rise. For a company, that means planning non-urgent moves for quieter times, consolidating small coins when that will shrink later payments, knowing how replace-by-fee and child-pays-for-parent work, and testing a small amount before a large payment. Hold coins in a 2 of 3 multisig or with a regulated custodian.

What the mempool is

Bitcoin developer documentation describes the memory pool as the set of unconfirmed transactions a full peer keeps because they are eligible to be included in a later block. Bitcoin Core stores them in non-persistent memory, "calling them a memory pool or mempool". When a peer shuts down, "its memory pool is lost except for any transactions stored by its wallet". Unconfirmed transactions that are never mined "tend to slowly disappear from the network as peers restart or as they purge some transactions to make room in memory for others".

So the mempool you see in a block explorer is that explorer's view of the unconfirmed transactions its own nodes have accepted. Another node can have a slightly different list. There is no single global mempool.

Source: Bitcoin developer documentation: P2P network guide: transaction relay and the memory pool.

How miners pick transactions, and why fees rise

A bitcoin fee is not a fixed charge. It is the difference between the coins a transaction spends and the coins it pays out. What miners compare is the fee rate: satoshis per virtual byte. Bitcoin Core defines a fee rate as "Fee rate in satoshis per virtualbyte" (sat/vB). Virtual size follows BIP 141 (Segregated Witness): witness data is discounted, and the result is rounded up.

The Bitcoin transactions guide says fees per byte "are calculated based on current demand for space in mined blocks with fees rising as demand increases", and that "it is ultimately up to each miner to choose the minimum transaction fee they will accept". Bitcoin Core's mempool design then sorts unconfirmed transactions so that the highest feerate subsets come first, and it uses that order "for both block building and eviction, by selecting chunks at the front of the linearization when constructing a block template".

When many transactions are waiting, a payment that offers only a low sat/vB rate can sit unconfirmed for a long time. When the mempool is thin, the same payment may be included sooner at a lower rate. That is a description of how block space is allocated, not a prediction of the bitcoin price.

Source: Bitcoin Core src/policy/feerate.h: fee rate in satoshis per virtual byte, Bitcoin BIPs: BIP 141: Segregated Witness (consensus layer), Bitcoin developer documentation: Transactions guide: transaction fees and change, Bitcoin Core doc/policy/mempool-design.md: mining and eviction by feerate.

What this means for a company moving coins

A treasury policy cannot control the fee rate. It can only decide when a move is urgent, how coins are packaged, and how a stuck payment will be handled. The notes below are operational, not a recommendation to transact.

• Plan non-urgent moves for quieter times. If a payment can wait, use a current public fee estimate and consider waiting for a lower suggested rate rather than always paying the next-block estimate. This is about network fees, not about timing the bitcoin price.
• Consolidation. A company payment spends one or more unspent outputs (UTXOs). Many small outputs make later transactions larger, and a larger transaction costs more at the same sat/vB rate. Combining small outputs into fewer, larger ones when fee rates are lower can reduce the cost of later payments. See fees and UTXO housekeeping.
• Replace-by-fee (RBF). If a sent payment is still unconfirmed, the sender may be able to sign a replacement that spends the same inputs and pays a higher fee, so that nodes replace the original in their mempools. Bitcoin Core documents the conditions (the replacement must pay at least as much absolute fee as the original transactions, plus enough extra to cover its own bandwidth, and it must improve the mempool's feerate diagram). Wallet support varies. A recipient who treats an unconfirmed payment as settled takes a risk that a replacement could supersede it. See BIP 125 and Bitcoin Core mempool replacements.
• Child-pays-for-parent (CPFP). A later transaction that spends an output of the unconfirmed payment can pay a high fee, so that miners who want the child also take the parent. Bitcoin Core's package policy describes this as fee-bumping by CPFP. The child can be built by the sender (from change) or, in some cases, by the recipient. Wallet support varies. See Bitcoin Core package mempool accept.
• Test a small amount first. Before a large payment to a new address, or a new withdrawal path from an exchange or custodian, send a small test amount, wait for confirmation, and only then send the rest. See custody practices, sending bitcoin safely, and the yearly recovery drill.

For a company treasury, the usual custody choices on this site remain a 2 of 3 multisig or a regulated custodian. A single-key wallet is a single point of failure. See custody options and multisig for a company.

The six-step walkthrough of a company payment, including the mempool stage, is in how a transaction works.

How to read mempool.space

mempool.space is a widely used public explorer for the bitcoin mempool, recent blocks and fees. Three views are especially useful when a company is planning a move:

• Fee estimates. The site publishes currently suggested fee rates for new transactions. The live panel above reads the same public endpoint, documented as "GET Recommended Fees": "Returns our currently suggested fees for new transactions." See the recommended-fees API docs.
• Projected blocks. The homepage shows the current mempool arranged as projected blocks: a picture of how waiting transactions might fill upcoming blocks if they were picked by fee rate. The API describes this as "Returns current mempool as projected blocks." See the mempool blocks fees API docs and the dashboard at mempool.space. This is a projection from the explorer's own mempool, not a guarantee of which transactions will be mined.
• Price graph. The Bitcoin Price graph shows historical prices. Use the currency control on that page for US dollars or pounds sterling. Historical prices are also documented in the historical-price API docs. A price history is not a forecast.

The software that runs mempool.space is The Mempool Open Source Project, licensed under the GNU Affero General Public License version 3 (or any later version approved by a proxy statement published on its About page). It can be self-hosted. The official Terms of Service say the mempool.space website and its API services "are operated by Mempool Holdings S.A. de C.V. in El Salvador". The project is funded by community and enterprise sponsors, not by advertising: the About page invites individuals and businesses to become sponsors, and the official enterprise page describes higher API limits and related services. The public REST API is rate-limited (HTTP 429 if you exceed the limits; repeated excess may lead to a ban). The Terms provide the site and API "as is, as available", with no guarantee of accuracy. Numeric free-tier rate limits are not stated on the REST docs page.

Read more on the official About, Terms of Service, Mempool Enterprise and community sponsor pages, the GitHub repository and its LICENSE, and GitHub Sponsors.

UK: recording network fees

This section is about what official HMRC pages say. It is not accounting or tax advice. Confirm the current treatment with the company's accountant.

In the Corporation Tax chapter of the Cryptoassets Manual, CRYPTO41300 (allowable costs) states HMRC's view that the costs which can be deducted under section 38 of the Taxation of Chargeable Gains Act 1992 include "transaction fees paid for having the transaction included on the distributed ledger", as well as the sterling consideration originally paid for the asset and certain other incidental costs. That is the primary text we have found for a company calculating a chargeable gain or loss.

Separately, CRYPTO41250 says there is no disposal "if the company retains beneficial ownership of the tokens throughout the transaction, for example moving tokens between public addresses that the company beneficially controls (commonly described as moving tokens between wallets)".

What we have not found, and so cannot confirm: CRYPTO41300 is written for costs used when calculating a disposal. Those two pages do not spell out how a network fee on an internal move (which CRYPTO41250 says is not a disposal) is treated for Corporation Tax. We have also not found a primary FRS 102 or FRS 105 paragraph that says how a company should book a bitcoin network fee in its statutory accounts. CRYPTO40100 does say that taxable profits are calculated in pounds sterling, that a consistent valuation method should be used, and that records of the methodology should be kept. Keep a record of each network fee and ask the company's accountant how to show it in the books and on the return. See also UK accounting under FRS 102 and company tax on bitcoin.

US: recording network fees

This section is about what official IRS and eCFR pages say. It is not tax advice. Confirm the current treatment with a US tax adviser.

26 CFR 1.1001-7 defines "digital asset transaction costs" as "the amounts paid in cash or property (including digital assets) to effect the sale, disposition or acquisition of a digital asset", and says those costs "include transaction fees, transfer taxes, and commissions". The same section says that if digital assets "are used or withheld to pay digital asset transaction costs", that use or withholding "is a disposition of the digital assets for services".

The IRS frequently asked questions on digital asset transactions, FAQ 53 (added 15 December 2025), give the same idea in plainer words: digital asset transaction costs "may include transaction and “gas” fees, transfer taxes, and commissions". But "if you pay costs to effect a transfer of digital assets, rather than a purchase, sale, or disposition, those costs are not treated as digital asset transaction costs". The example given is "amounts paid by you for transaction services to effect a transfer of your digital assets between your own wallets or accounts".

FAQ 81 (also added 15 December 2025) says that a transfer from a wallet, address or account belonging to you to another that also belongs to you "is a non-taxable event, except to the extent of any digital assets you use, or are withheld, to pay for transaction services to effect the transfer".

In short, for a sale or purchase the official sources treat network or "gas" fees as transaction costs that can enter the gain or loss computation, and paying those costs in bitcoin is itself a disposition of the bitcoin used. For a move between wallets the company already controls, the move is generally not a taxable event, but bitcoin used to pay for the transfer is carved out in FAQ 81, and FAQ 53 says those transfer-service costs are not "digital asset transaction costs". How that carve-out should be reported in a particular company's return is a question for its adviser. See also US accounting under ASU 2023-08 and company tax on bitcoin.

Read next

• How a transaction works, including the mempool stage of a company payment.
• Fees and UTXO housekeeping, size, fee rate and consolidation.
• Market and network context, live price, fees and hash rate, data only.
• Custody options, 2 of 3 multisig or a regulated custodian.
• Recovery drill, a yearly 2 of 3 test with a record sheet.
• Sending bitcoin safely, checks before every payment.

Sources

Primary sources only. Each link was checked on 11 November 2026. Rules change, so confirm the current version with your adviser.

1. Bitcoin developer documentationP2P network guide: transaction relay and the memory pool
2. Bitcoin developer documentationTransactions guide: transaction fees and change
3. Bitcoin Coresrc/policy/feerate.h: fee rate in satoshis per virtual byte
4. Bitcoin BIPsBIP 141: Segregated Witness (consensus layer)
5. Bitcoin Coredoc/policy/mempool-design.md: mining and eviction by feerate
6. Bitcoin BIPsBIP 125: Opt-in full replace-by-fee signalling
7. Bitcoin Coredoc/policy/mempool-replacements.md: current replace-by-fee policy
8. Bitcoin Coredoc/policy/packages.md: package mempool accept and fee-bumping by CPFP
9. mempool.spaceREST API documentation: GET Recommended Fees
10. mempool.spaceREST API documentation: GET Mempool Blocks Fees (projected blocks)
11. mempool.spaceBitcoin Price graph (USD or GBP via the currency control)
12. mempool.spaceAbout: The Mempool Open Source Project, sponsors and licensing
13. mempool.spaceTerms of Service (updated 10 July 2024): operator, no warranty, no advertising
14. mempool.spaceMempool Enterprise
15. GitHubThe Mempool Open Source Project LICENSE: GNU AGPL v3
16. HMRCCRYPTO41300: Corporation Tax, allowable costs, including transaction fees on the distributed ledger
17. HMRCCRYPTO41250: moving tokens between addresses the company beneficially controls is not a disposal
18. HMRCCRYPTO40100: conversion to sterling and accountancy, records of the valuation methodology
19. eCFR26 CFR 1.1001-7: digital asset transaction costs and disposition when digital assets are used to pay them
20. IRSFAQs on digital asset transactions: Q53 (transaction costs) and Q81 (transfers between your own wallets)