What is Bitcoin halving?
Bitcoin halving is the mechanism that cuts the new-coin subsidy available for each new block in half according to a predetermined rule. It occurs every 210,000 blocks, usually about every four years. The reduction applies to newly issued bitcoin, not bitcoin (BTC) users already hold, and does not include transaction fees.
How does halving happen?
After miners produce a valid block adopted by the network, they can claim the block subsidy and transaction fees. The subsidy is new issuance, and its limit depends on block height; block height is a block’s position in the chain.
Bitcoin mainnet began with a subsidy of 50 BTC per block. Every 210,000 blocks, the subsidy for subsequent blocks halves: 50, 25, 12.5, 6.25, 3.125 BTC…
For example, the subsidy limit at height 839,999 is still 6.25 BTC; at height 840,000 it becomes 3.125 BTC. Nodes, computers running the network’s validation software, check block rewards against the applicable rules and reject blocks that claim too much. Exchanges therefore do not need to initiate a separate operation on halving day.
Why is it described as happening about every four years?
Bitcoin targets an average block interval of ten minutes. At that pace, 210,000 blocks take about four years, hence the common description of a four-year halving cycle.
However, block production is random, and changes in the network’s total hash rate—the combined rate of computational attempts per unit of time—also affect the actual pace. The network adjusts difficulty based on past block times to keep the long-term average near the target, rather than guaranteeing that each block arrives on schedule.
The halving height is therefore known, while its exact date can only be estimated as actual block production progresses. Halving adjusts the subsidy; it does not directly change the target block interval.
When did past halvings occur, and when is the next one?
The dates of completed halvings below are converted from the corresponding block timestamps to Coordinated Universal Time (UTC). The year of the fifth halving is an estimate. Each subsidy shown is the new limit applying from that height onward.
Halving | Block height | Date (historical dates in UTC) | Subsidy per block after halving |
|---|---|---|---|
First | 210,000 | 2012-11-28 | 25 BTC |
Second | 420,000 | 2016-07-09 | 12.5 BTC |
Third | 630,000 | 2020-05-11 | 6.25 BTC |
Fourth | 840,000 | 2024-04-20 | 3.125 BTC |
Fifth (estimated) | 1,050,000 | Around 2028; exact date undetermined | 1.5625 BTC |
The fourth halving fell on April 19 in some time zones. If you encounter different dates, check the time zone first.
Under the current rules, the next halving triggers at height 1,050,000. Its exact date depends on actual block production. The year in the table is neither a fixed date nor a live countdown.
How does halving affect Bitcoin issuance?
Halving progressively reduces the BTC issued in each period. For example, the total subsidy limit for the first 210,000 blocks is 10.5 million BTC; the next period allows 5.25 million, then 2.625 million, with further reductions afterward.
This issuance sequence produces the commonly cited cap of about 21 million BTC. Calculations actually use satoshis: 1 BTC equals 100,000,000 satoshis, and fractions below one satoshi are discarded. The total subsidy limit is therefore slightly below 21 million. This is not the current circulating supply; underclaimed subsidies and unspendable funds, among other factors, also affect actual quantities.
The subsidy eventually reaches zero. The commonly cited year “around 2140” is likewise an estimate based on block production speed, not a calendar deadline specified by the protocol. Users’ existing BTC do not decrease because of halving, and transaction fees do not automatically disappear when the subsidy reaches zero.
What does halving mean for miners?
Halving directly reduces the new-coin subsidy miners can claim each time they successfully produce a block. Their total revenue also includes fees, while operating results depend on their share of block production, the coin’s price, electricity and equipment costs. It therefore cannot be assumed that revenue or profit necessarily falls by exactly half.
As the subsidy declines, fees become more important to revenue, but their amount and share still fluctuate. A zero subsidy does not shut down mining at the protocol level. How much hash rate future fees can support depends on transaction demand and costs at that time, among other conditions. For the revenue components, see block rewards.
Does halving cause prices to rise?
Halving reduces the rate of new issuance, but does not directly determine the market price. Prices also depend on buying and selling demand, market expectations, liquidity and the macroeconomic environment.
The halving rule is known in advance, so participants may trade on it before the event. Even if prices rose during some past periods, halving alone cannot establish the size or timing of future gains. Nor should the roughly four-year subsidy cycle be treated as a fixed price cycle.
Related terms
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