Why pools exist
Finding a block is a lottery. A miner with a small share of the network’s total computing power might wait months or years between wins, and the reward is large when it comes. That makes income extremely lumpy: a miner could pay electricity bills for a long time and see nothing. A mining pool solves this by combining the work of many miners and splitting the rewards in proportion to contribution. Individual miners trade a small fee and some control for much steadier income.
How a pool works
A pool operator runs a server that prepares candidate blocks and hands out work. Members’ machines hash and report back. To prove they are doing real work, miners submit shares, which are hashes that meet an easier target than the real one. A share is not a valid block, but because shares are found far more often, the pool can count them to measure each member’s contribution. Occasionally one of the hashes also meets the full network target, and that block is submitted, earning the reward for the whole pool.
Common payout methods
Pools differ in how they distribute the money, and the main differences are who carries the luck risk:
- Pay per share. The pool pays a fixed amount for each valid share, regardless of whether it finds blocks. The pool operator carries the variance, so the fee is usually higher.
- Proportional and similar schemes. When a block is found, its reward is divided by the shares submitted in that round.
- Pay per last N shares. Rewards are split across the most recent shares, not just one round, which discourages members from hopping between pools.
- Variants that also pay out an estimate of fees. Some methods include transaction fees in the fixed payout and others do not.
The details change over time and differ by pool, so a miner would need to read the terms of any pool they consider. Fees are typically a small percentage.
Pooling does not increase the total reward
Joining a pool does not make the miner earn more in the long run. Expected income is, roughly, the same share of the network total minus fees. What changes is variance, meaning how smooth the earnings are. This distinction is easy to miss: pools reduce the risk of long dry spells, not the economics of mining. Costs and margins still decide whether mining is worthwhile, as the production cost article describes.
Hash rate distribution
When people say hash rate is distributed in some way, they usually mean how the blocks found recently split among pools. Data websites estimate this by looking at who is credited in each block, often through identifying marks that pools leave in the coinbase transaction or by known payout addresses. This works reasonably well for large public pools but has limits:
- Some pools do not label their blocks, so they can be missed or guessed.
- One company may run several pool brands, or a pool may have members spread across many countries.
- Short samples are noisy, because block finding is random. A small number of blocks in a week can look like a big swing in share.
For these reasons, shares quoted in charts are approximate and move around. The aggregate computing power itself is discussed in the hash rate article.
Decentralization concerns
Bitcoin’s security rests on no single party controlling a majority of the mining power. If one pool reached a large share, its operator could, in principle, try to reorder recent transactions or block specific ones, or participate in a majority attack. Large pool share does not mean the operator owns the hardware, though. Members can leave a pool whose operator misbehaves, and a pool that is seen to cross a worrying threshold has historically faced pressure to shrink as miners moved elsewhere. This is a social check, not a technical guarantee, and it relies on miners paying attention.
Another question is who decides which transactions go into a block. In a pooled setup, the operator traditionally builds the candidate block and members only supply hashing. Some newer protocols allow members to build their own templates, which would spread the decision-making more widely; adoption has varied and the details are still evolving.
There are also arguments that the pool picture overstates concentration. Members of a large pool are separate businesses and individuals with their own interests, and hardware manufacturers, hosting companies and electricity markets add other points where power can concentrate. Opinions differ on which of these matters most.
Pools, fees and the long term
As block subsidies fall over time and fee revenue becomes more important, the way pools handle fees and the ordering of transactions may matter more. How these incentives play out is not known.
Reading pool charts sensibly
- Treat percentage shares as rough estimates.
- Look at longer windows to smooth out luck.
- Remember that a share of blocks is not the same as ownership of machines.
- Do not treat shifts in pool shares as price signals; no reliable link has been shown.
Cryptocurrency prices are volatile and people can lose all they invest. This article is educational and is not financial, tax or legal advice.