Miners add and remove machines all the time, yet blocks keep arriving about every ten minutes. The reason is the difficulty adjustment, built into every node.
The target
A block is valid only if its header hash is below a target number. A lower target means fewer valid hashes, so more attempts are needed. The header stores the target in a compact 4-byte form called nBits. "Difficulty" is just a human-friendly ratio: how much harder the current target is than the easiest allowed target.
Every 2,016 blocks
After every 2,016 blocks, each node compares how long they took with the planned two weeks (2,016 × 10 minutes). If they came in one week, the target is halved, which doubles the difficulty. If they took four weeks, the difficulty is halved.
Guard rails
- One adjustment can change difficulty by at most a factor of 4 up or down.
- Satoshi's code measures the time between the first and last block of the period, which covers only 2,015 block intervals. This small off-by-one is still part of the rules.
- Block timestamps must be later than the median of the previous 11 blocks, and nodes reject blocks more than two hours ahead of their own clock. That limits how far miners can game the clock.
No central control
Nobody sets the difficulty. Every node calculates it from the chain itself and rejects any block with the wrong target. A miner that cheats on the target simply creates an invalid block.
Real-world swings
When China banned mining in 2021, hash rate dropped sharply and difficulty fell by about 28% in one adjustment, one of the largest drops in Bitcoin's history. Most of the time, changes are a few percent.
As of 23 October 2026, difficulty was about 140.6 trillion, according to mempool.space. The last adjustment was about +5.9%, and the next one was expected near block 973,728. Estimates like that change by the hour.
Why it matters
The adjustment keeps the issuance schedule on track no matter how much hardware joins. It also means more hash power makes Bitcoin harder to attack, not faster to mine.