Mining difficulty

How does it work?

Miners look for a HashHashA short fingerprint calculated from data, which changes completely if the data is altered by even a single character. that is lower than a certain target. The lower the target, the less often a guess hits it, and the higher the difficulty.

Think of rolling two dice. If you need a total below 3, you will rarely manage it. If anything below 10 will do, you will succeed most of the time.

Adjusted about every two weeks

Every 2,016 blocks, the network's nodes compare how long those blocks took with the two weeks they should have taken:

• If the blocks were found too quickly, the difficulty goes up.
• If they were found too slowly, it goes down.

Each adjustment can at most quadruple the difficulty or cut it by 75%. In this way it follows the network's HashrateHashrateThe total number of guesses a network's mining computers make each second, and a measure of how well the network is protected from attack.: when more machines join, it rises, and when machines switch off, it falls.

An example

In spring 2021, the Chinese authorities began cracking down on mining, and a large share of the network's machines were switched off. For a while, blocks were found much more slowly. On 3 July 2021, the difficulty fell by almost 28%, the largest drop in Bitcoin's history. After that, blocks were found at the normal pace again.

What to keep in mind

The difficulty is what keeps the issuance of new bitcoin on a fixed schedule, because the block rewardBlock rewardWhat a miner receives for adding a block to the chain: newly created bitcoin plus the network fees in the block. is paid out roughly every ten minutes. More machines don't speed up issuance in the long run. What they do is make the network more expensive to attack.