Who decides which Bitcoin payments are real? No bank does, and no single company does either. Proof of work is the rule that answers that question. It is the system Bitcoin uses to pick who adds the next block of transactions, and it works by making that job cost real money. Computers called miners race to guess a number, the first one to find it adds the block, and cheating would mean outspending every honest miner at once. That cost is the whole point, and it is what has kept Bitcoin running without a boss since 2009.
Key points:
- Proof of work picks the next block by a guessing race. Miners burn electricity to find a winning number, and the first one to find it adds the block.
- The puzzle gets harder as more miners join, so a new Bitcoin block still lands about every 10 minutes.
- Rewriting an old payment would mean redoing all that work. That is why Bitcoin has never been hacked at the protocol level.
How does a miner actually win a block?
Miners start by collecting pending transactions and packing them into a candidate block. Then they change a small number in the block, called a nonce, and run the whole block through a hash function, which spits out a digital fingerprint. They repeat it with a new nonce each time, hunting for a fingerprint below a target number the network sets. A modern mining machine makes more than 200 trillion guesses a second, and the first miner to land under the target wins the block.
A lot of people picture miners solving clever maths problems. They are not. They are guessing, trillions of times a second, until one guess lands under the target. The puzzle is not hard to understand. It is hard to win, because everyone else is guessing too. Once a miner wins, it sends the block out, the network checks it with a single hash, and the winner collects the block reward plus the fees inside the block. Since the April 2024 halving, that reward is 3.125 bitcoin per block.
Why does the network make the puzzle harder?
Left alone, faster machines would find blocks faster and faster. So Bitcoin checks itself every 2,016 blocks, about two weeks, and resets the difficulty so blocks keep averaging 10 minutes. When more miners join, the target tightens. When miners switch off, it loosens again. In late October 2026, the difficulty rose 5.54% to about 148 trillion, because the previous 2,016 blocks had arrived faster than the two-week schedule.
This self-balancing act is what makes the system steady. It does not matter how many miners show up or how fast their machines get. The target just moves until a block takes 10 minutes again.
Read also: What Is Proof of Stake? How Blockchains Stay Honest Without Mining
What stops someone from rewriting history?
Changing an old payment would mean redoing the work for that block and every block after it, faster than all the honest miners put together. That is the idea behind a 51% attack, and the price of trying it is why it has never worked against Bitcoin. The chain has run since 2009 with no successful attack on the protocol itself. Figures for what an attack would cost are estimates from researchers, not audited facts, so treat them as a rough guide, not a price tag. But the direction is clear. The bigger the network grows, the dearer an attack gets.
Which coins still use proof of work?
Bitcoin is the biggest by far, but it is not the only one. These four still run on proof of work today.
| Coin | Launched | Puzzle | Block time |
|---|---|---|---|
| Bitcoin | 2009 | SHA-256 | About 10 minutes |
| Litecoin | 2011 | Scrypt | About 2.5 minutes |
| Dogecoin | 2013 | Scrypt | About 1 minute |
| Monero | 2014 | RandomX | About 2 minutes |
Ethereum ran on proof of work too, until it switched to proof of stake on 15 September 2022, in an event called the Merge. The Ethereum Foundation puts the energy saving at about 99.95%, because validators lock up coins instead of burning power.
Is proof of work worth the power bill?
This is the fair question, and the honest answer starts with the size of the bill. The Cambridge Bitcoin Electricity Consumption Index put Bitcoin's power use at a best guess of about 174 terawatt-hours a year on 2 November 2026, inside a wide range of roughly 90 to 335 terawatt-hours. The range is wide because nobody can meter every miner on earth, so take any single number with a pinch of salt. For scale, that best guess sits near the yearly power use of a mid-size country.
My own read is that the power bill is not waste, it is the security budget. You can hate the size of the bill and still see what it buys. It buys a ledger no government or company controls. The honest question is not whether the power is used, it is whether what it protects is worth that much power. For the world's biggest crypto network, most holders have answered yes so far.
What to watch next
If you want to judge proof of work for yourself, write down three numbers today, then check them again in a month. First, the difficulty, near 148 trillion in late October 2026, which resets about every two weeks. Second, the network hashrate, which shows whether miners are joining or switching off. Third, the block reward, 3.125 bitcoin until the next halving in 2028. If you ever think about mining yourself, write down your electricity price first. That one number decides whether mining pays at all. A rising difficulty with a steady hashrate means a healthy network. A sharp fall in hashrate is the warning to watch.
Read also: What Is an ASIC Miner? A Simple Guide to Crypto Mining
— BitByLine News Desk
This post is for learning only. BitByLine explains and teaches, and this is not financial advice. We never tell anyone to buy or sell crypto. Whether you buy or not is your own decision, and the risk is yours too. Always do your own research first. Read our full Disclaimer.
Sources: Sonic Wallet, SimpleMining, KryptoKraken, CoinCentral, Cambridge Centre for Alternative Finance.
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