Mining difficulty
Also called: network difficulty, difficulty adjustment
Mining difficulty sets the effort needed to find a block. The network adjusts it to keep block production at a steady pace.
Mining difficulty sets how hard it is to find a valid hash for a block. In concrete terms, the network sets a target: the block's hash must be lower than this number. The lower the target, the more attempts it takes on average, and the higher the difficulty. It is the same for every miner on the network, big or small.
On Bitcoin, the difficulty is recalculated every 2,016 blocks, roughly every two weeks. The aim is to keep one block about every 10 minutes. If new machines join and blocks come out faster, the difficulty goes up; if miners shut down, it goes down. Other coins have their own adjustment rules, sometimes recalculated at every block, as on Kaspa.
For anyone buying a machine, difficulty is the great unknown. With the same hashrate, a higher difficulty means less coin earned. Historically, Bitcoin's difficulty has tended to rise as more powerful machines arrive, even though it sometimes falls back. A profitability estimate is therefore only valid at the moment it is calculated: redo it regularly and favor the most efficient machines, which hold up better against increases.
Our Bitcoin profitability calculator uses the network difficulty at the time of your simulation.