What do Bitcoin miners actually do? A plain guide to mining

A Bitcoin (BTC) miner runs special computers that race to add the next batch of transactions, called a block, to the shared ledger known as the blockchain. The winner gets paid in new bitcoin. That payment, 3.125 BTC per block since April 2024, is the reward for doing the work that keeps the network running and hard to cheat. No bank sits in between.

What a Bitcoin miner actually does

Mining is bookkeeping with a prize attached. About every ten minutes, miners gather recent transactions, bundle them into a block, and compete to seal that block onto the chain. The machines doing this are not normal PCs. They are ASICs, chips built for one job: computing the same math puzzle over and over, billions of times a second.

The puzzle has no clever shortcut. A miner changes one small number in the block, a value called the nonce, runs the whole block through a hashing function, and checks the result. If that result is a small enough number, the block counts, and the miner sends it to everyone. If not, the miner tries again. "The mining hardware iterates through every possible value for the block header nonce and generates the corresponding hash," the Bitcoin project's developer guide says.

It is trial and error. Nothing clever. Just raw speed and electricity, repeated until someone wins the round.

Winning matters because the first miner to find a valid block gets two things: new bitcoin and the fees attached to the transactions inside it. Other computers on the network, called full nodes, run software such as Bitcoin Core and check that work. If the block breaks a rule, they throw it out, and the miner burned power for nothing.

Across the whole network, miners together make an astronomical number of these guesses every second, all racing for the same block. Almost all of that effort is thrown away. Only one machine wins each round. The rest start over at once on the next block, with a fresh batch of transactions.

Proof of work, in plain terms

This system has a name: proof of work. The idea is old and simple. Making a valid block has to be expensive, so that lying about the history of payments costs more than it could ever earn.

Think of it like a lottery where buying more tickets means burning more power. A miner with more machines gets more guesses each second, so it wins more often. No single guess is ever a sure thing. A small operation can still find a block. It just happens rarely.

This is what stops anyone from quietly rewriting old transactions. To change a block from last year, an attacker would have to redo its proof of work and then out-race the entire rest of the network to catch up. The deeper a payment sits under newer blocks, the harder it is to undo. Pulling that off would need more computing power than everyone else on the network combined, kept up for as long as the race lasted.

That security is not free, and it is not magic. It is paid for in machines and electricity. That is the whole design, and also the loudest complaint against Bitcoin.

The block reward and why it keeps shrinking

New bitcoin enters the world one way only: through mining. Each block creates a set amount, called the subsidy. It began at 50 BTC per block back in 2009. It is now 3.125 BTC.

That drop is written into the rules. Roughly every four years, the subsidy is cut in half, an event known as the halving. The most recent one landed at block height 840,000 on April 20, 2024, when the reward fell from 6.25 BTC to 3.125 BTC, according to The Block. "The Bitcoin reward is divided by 2 every 210,000 blocks, or approximately four years," Blockchain.com notes.

Each halving shrinks the new supply a little more. Sometime around the year 2140, the subsidy reaches zero and no fresh bitcoin is minted. The total cap is 21 million coins. Once the subsidy runs out, miners will earn only the fees that users pay to get into a block.

Those fees are small today, but they climb when the network is busy. When blocks fill up, users bid against one another to get in, the way drivers pay extra for a fast lane at rush hour. For most of Bitcoin's life the subsidy has far outweighed the fees, so the shrinking reward is a slow question about miners' future income, not a problem for today.

Difficulty, and why blocks still arrive about every 10 minutes

More miners join when the price of bitcoin rises. More machines mean more guesses each second, which on its own would make blocks arrive faster and hand out new coins too quickly. The network stops that with a lever called difficulty.

Every 2,016 blocks, roughly two weeks, the software measures how long those blocks actually took and resets the target. "The ideal value is 1,209,600 seconds (two weeks)," the developer guide states. If miners were too fast, the puzzle gets harder. Too slow, and it eases off. The goal is to hold the average near one block every ten minutes, whatever computing power is aimed at the network.

So the pace stays steady. The effort does not. More power pointed at Bitcoin does not mean faster blocks, only a harder puzzle.

What mining costs in electricity

All that guessing burns a lot of power, and the totals are big enough to draw steady criticism. The Cambridge Centre for Alternative Finance put Bitcoin's yearly electricity use at about 138 TWh in a report dated 28 April 2025, which it said was roughly 0.5% of the world's total. The same study pegged the network's emissions at 39.8 MtCO2e.

Where that power comes from is changing. Cambridge found that sustainable sources, nuclear plus renewables such as hydropower and wind, made up 52.4% of the mix. Natural gas was the single biggest fuel at 38.2%, up from 25.0% in 2022. Coal, once the largest source, had slipped to 8.9%.

In the United States, the government has tried to size up its own share. The US Energy Information Administration estimated that crypto mining used between 0.6% and 2.3% of American electricity, or about 25 to 91 TWh a year, based on 2023 activity. The range is wide because miners move around, shut off when power is pricey, and do not all report what they draw. To put that in perspective, the EIA said that much power could run somewhere between three million and six million American homes for a year.

Critics read these figures as pure waste. Miners answer that they often run on power nobody else wants, stranded gas or spare hydro, and that they can switch off in seconds when the grid is under strain. Both things can be true at once.

Solo miners, pools, and where mining happens

Finding a block alone is now close to hopeless for a small player. The odds are so long that a lone home rig might wait years for a single win. So most miners join a pool.

A pool combines the power of thousands of machines and splits the reward by how much work each member added. "The miner pools resources with other miners to find blocks more often," the developer guide explains. The block reward and fees flow to the pool, which then pays its members.

Geography matters as well. The Cambridge survey, which covered 49 mining firms across 23 countries and about 48% of the network, found the United States running 75.4% of the activity those firms reported. An earlier EIA estimate had put the US at roughly 38% of global mining in 2023. The map keeps moving as miners chase cheap power. Operators care about one thing above all, the price of electricity, because power is their largest running cost.

What to keep in mind

Mining is the engine room of Bitcoin. It is also the part people fight over most, because it turns electricity into both security and new coins at the same time.

For a regular user, none of this is something you do by hand. You do not need to mine to hold or send bitcoin, any more than you need to run a bank's servers to keep a dollar. Still, it helps to know who does the work, what they earn, and why the reward keeps shrinking.

Nobody can change these rules on a whim. The math does not bend. And the reward gets smaller every four years, right on schedule, until the last coin is mined.