How Is the ‘Difficulty’ of a Cryptocurrency Network Adjusted over Time?

Network difficulty is a measure of how hard it is to find a hash below a certain target. It is automatically adjusted by the network's protocol to ensure a consistent average block time, regardless of the total hash rate on the network.

For Bitcoin, this adjustment happens roughly every 2016 blocks, or about every two weeks. If the time between blocks is too fast, difficulty increases; if too slow, it decreases.