The Difficulty Adjustment

Bitcoin is designed to produce one block every ten minutes on average. Not nine minutes. Not eleven. Ten.

This sounds simple until you consider the complication: the amount of mining power on the network changes constantly. More miners join as the price rises. Miners leave during bear markets. China banned mining in 2021 and half the global hash rate disappeared in weeks. New hardware gets deployed. Old hardware gets retired.

If the target difficulty never changed, more mining power would mean faster blocks. Less mining power would mean slower blocks. The ten-minute average would be meaningless.

Satoshi’s solution was the difficulty adjustment. Every 2,016 blocks — roughly two weeks — Bitcoin looks at how long those blocks actually took to find. If they came faster than ten minutes on average, the target gets harder. If they came slower, it gets easier. The network self-corrects, continuously, without any human making a decision.

When China banned Bitcoin mining in 2021 and hash rate dropped by roughly 50% overnight, blocks started coming every twenty minutes. Two weeks later, the difficulty adjusted downward. Blocks returned to their ten-minute rhythm. The network didn’t skip a beat.

No CEO ordered this. No vote was taken. The code executed as designed, as it has every two weeks since 2009.

The difficulty adjustment is one of Bitcoin’s least-discussed features and one of its most important. It’s what makes the ten-minute block time a reliable property of the network rather than a hopeful average — regardless of how much computing power the world throws at it.

Tomorrow: what is a node — and what does it actually do all day?

— The Daily Bit