Definition
The bitcoin halving is a built-in protocol event that cuts the number of new bitcoin paid to miners for each block in half. It happens every 210,000 blocks, which works out to roughly every four years.
How it works
A miner who adds a block to the Bitcoin blockchain receives a block reward with two parts: the block subsidy, which is newly created bitcoin, and the transaction fees paid by users. The protocol halves only the subsidy, every 210,000 blocks. It started at 50 BTC per block and halves each time: 50 → 25 → 12.5 → 6.25 → 3.125 BTC and so on, until the subsidy is too small to divide further. Transaction fees are not halved.
Blocks are found about every 10 minutes on average, so 210,000 blocks take roughly four years. The exact date of a halving cannot be known in advance; it is estimated from the current block height and the recent pace of block production, and the estimate shifts as that pace changes. Each halving slows the creation of new coins, so total supply approaches the 21,000,000 cap more and more slowly.
Halvings reduce the flow of new coins into the market and cut miners' income from the subsidy, which can push less efficient miners to stop. Price behaviour around past halvings is widely discussed, but there have been only a few of them and other factors moved the market at the same time, so past patterns are no guarantee of future results.
Example (hypothetical numbers)
Suppose the block subsidy is 3.125 BTC, blocks average 10 minutes, and each block also carries 0.25 BTC in transaction fees.
Blocks per day ≈ 24 × 60 ÷ 10 = 144, so new issuance ≈ 144 × 3.125 = 450 BTC a day, and after the next halving 144 × 1.5625 = 225 BTC.
Miner income per block falls from 3.125 + 0.25 = 3.375 BTC to 1.5625 + 0.25 = 1.8125 BTC.
That is a drop of (3.375 − 1.8125) ÷ 3.375 ≈ 46.3%, not 50%, because transaction fees are not halved.
The halving cuts new issuance by exactly half, but cuts miner income per block by less whenever fees are present.
Common mistakes
- Treating a projected halving date as fixed, when it depends on how fast blocks are actually found.
- Assuming the halving also cuts transaction fees or miners' total income by exactly half.
- Expecting price moves after past halvings to repeat after the next one.
Related calculators
This glossary is for education only and is not investment advice. Examples use hypothetical numbers.