Difficulty is a number that tells miners how hard it is to find a valid block. It is Bitcoin's thermostat, keeping block times near ten minutes no matter how much computing power joins or leaves.
Target and difficulty
To win a block, a miner must produce a block-header hash lower than a target value. A lower target means fewer winning hashes, so more attempts are needed. "Difficulty" is a friendlier way to express this: it compares the current target with the easiest one ever used. A difficulty of 1 was the starting point in 2009. As of October 2026 it is about 140 trillion.
The adjustment
Every 2,016 blocks, roughly two weeks, every node runs the same calculation. It compares how long those blocks actually took with the expected 20,160 minutes. If blocks came too fast, difficulty goes up. If they came too slowly, it goes down. To prevent extreme jumps, each adjustment is limited to a factor of four in either direction.
Why it matters
Without it, adding more ASICs would make blocks arrive faster and faster, releasing new coins ahead of the halving schedule. With it, more hash power simply makes mining harder. That keeps the supply schedule on track and the network more secure.
A real-world test
In 2021, China banned mining, and around half of the network's hash power went offline within weeks. Blocks slowed down, then on 3 July 2021 the difficulty dropped by about 28 percent, the largest downward adjustment in Bitcoin's history. Block times returned to normal, and the network kept running without any central decision.
The difficulty is not set by anyone. It is an automatic rule in the code, and every full node checks it.