What Is Difficulty Adjustment?

In Bitcoin, difficulty is recalculated once every 2016 blocks, that is, about every two weeks. The protocol looks at how long it took to produce the last 2016 blocks: if blocks were found faster than the 10-minute target, the difficulty is increased; if slower, it is decreased. To limit sudden changes, difficulty can be increased or decreased by at most four times in a single adjustment. This way, even as new miners join the network, the rate at which new BTC enters the market stays predictable.

Difficulty adjustment is critical for the functioning of Bitcoin's monetary policy; even if the hash rate multiplies, the block production rate and the halving schedule are largely preserved. In 2021, when the hash rate fell sharply after the mining ban in China, blocks slowed for a while, and then the difficulty was readjusted with one of the largest drops in Bitcoin's history. This event showed how the mechanism balances the network on its own.

Different networks use different algorithms; some PoW networks update difficulty at every block. In small networks, sudden fluctuations in hash rate, combined with long adjustment intervals, can lead to large deviations in block times. In Proof of Stake (PoS) networks, because block production is tied to time slots, this kind of difficulty adjustment is not needed.