Retargeting

Retargeting is the process by which a proof-of-work blockchain recalculates its mining difficulty so that new blocks continue to be found at roughly the target pace, whatever the total computing power on the network. Bitcoin retargets every 2,016 blocks, about every two weeks. It compares how long those blocks actually took with the expected two weeks implied by its ten-minute block time, then raises or lowers the difficulty in proportion, with any single change capped at a factor of four. If the hashrate rises because more miners join, blocks come faster and difficulty goes up; if miners leave, as after China's 2021 mining ban, difficulty falls. Other networks retarget more often, some after every block, to react faster to sudden swings. In digital marketing, "retargeting" has an unrelated meaning: showing adverts to people who visited a website earlier.