Halving

A halving is a sudden reduction of the block subsidy, used by coins like Bitcoin to slow new supply on a fixed schedule. At each halving the per-block subsidy drops by half.

Bitcoin halves every 210,000 blocks, which takes about four years. It started at 50 BTC per block in 2009. The subsidy fell to 25 BTC in 2012, 12.5 BTC in 2016, 6.25 BTC in 2020 and 3.125 BTC in April 2024. Because the steps keep halving, total supply approaches but never passes 21 million BTC.

The halving falls on a block height, not a date. The date is only an estimate, because block times vary. A coin's explorer or the pool's stats show the current height, so you can count how many blocks are left.

For miners, a halving cuts the subsidy part of every block reward overnight. If the coin's price and fees stay the same, the same rig earns about half as much from the subsidy the next day. Transaction fees are not halved, so they become a larger part of the reward over time.

Difficulty does not drop on its own at a halving. It only falls if miners switch off because they are no longer profitable. Some do, and difficulty then eases at the next adjustment, which gives the remaining miners a larger share.

A common misconception is that every coin halves. Many do not. Some lower the subsidy a little with every block, a smooth decay, so there is no sudden step. Others settle at a small fixed reward forever, called a tail emission. Monero, for example, has paid a fixed 0.6 XMR per block since 2022.

Before a halving, check your costs. A rig that is only just profitable today may run at a loss after the subsidy halves. Look at the coin's emission schedule, which says whether and when its reward steps down, before you buy hardware for it.