A halving is a scheduled cut that reduces a blockchain's block subsidy by half at a fixed block interval. Bitcoin's subsidy began at 50 bitcoin per block and halves every 210,000 blocks, roughly once every four years, converging on a hard supply cap and a terminal state where the only payment for securing the chain is transaction fees. The rule lives in consensus code, so it applies automatically rather than by decision.
A halving is the most predictable supply event in the asset class and the least predictable revenue event for the people securing the chain. Everyone can see the date years out. The cost of running a mining rig does not halve alongside it.
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The rule, as it is written
Bitcoin's block subsidy started at 50 bitcoin and is halved every 210,000 blocks, which at a ten minute target block time works out to roughly four years. Blocks at a height of 6,930,000 or above are entitled to no subsidy at all.1 This is arithmetic in consensus code, not a policy anyone administers, and no participant has discretion over it.
Two properties follow directly. Supply is capped, because a geometric series of halvings sums to a finite total. And issuance is front loaded: the first epoch mints as much as every subsequent epoch put together. Adopting this shape is choosing to pay most of your lifetime security budget in your first few years, on the theory that the network will be worth more later and can pay in fees.
A halving is a supply rule, not a demand event
Every halving arrives with a wave of forecasting about what it will do to price. We do not make those calls, and we treat a design that depends on one as unfinished. What the rule does is cut the rate at which new units enter the market by half, on a date the entire world can compute in advance. What price does with information everybody already has is a separate question involving demand, liquidity and positioning, none of which the schedule touches.
The framing that is actually useful to a founder is narrower. A halving is a scheduled 50 percent cut to the revenue of the group doing the most expensive work on your network. Design around that, not around a price thesis.
What it does to an operator on the day
Mining revenue is denominated in the token. Electricity, hosting, hardware financing and payroll are denominated in fiat, and none of them halve. The moment the subsidy steps down, the operating margin of every miner on the network steps down with it, and the marginal machines stop paying for themselves.
The network's response is mechanical. Unprofitable hash rate switches off, difficulty adjusts downward at the next retarget, and the operators still running collect a larger share of a smaller pot. That is the design working as specified. The cost falls on the operators who exit, which is why each cycle concentrates mining toward whoever holds the cheapest power and the strongest balance sheet.
If you are designing a network whose participants carry real-world costs, study this pattern before writing a step into your own schedule. Our operator selling entry covers what those same fiat costs do to sell pressure in the years between the steps.
The security budget question the schedule creates
Halving toward zero means the subsidy eventually stops and transaction fees become the entire payment for securing the chain. Whether a fee-only regime is stable is an open question rather than a settled one, and it deserves to be treated that way in any document that touches it.
The most cited academic treatment is Carlsten, Kalodner, Weinberg and Narayanan, presented at ACM CCS in 2016. Modelling mining without a block reward, they find that fee-only incentives produce new and less stable equilibria: miners gain reasons to mine intermittently, to fork the chain in order to capture an unusually rich block, and selfish mining becomes profitable at lower hash rate thresholds than under a subsidy.4
The counter-design is a subsidy that never stops, which is what our tail emission entry covers. Bitcoin and Monero sit on opposite sides of the same question: one caps supply and relies on a fee market maturing in time, the other keeps issuing forever and accepts permanent dilution as the price of a predictable security budget. Both positions are coherent. Neither has been settled by evidence, because no chain of consequence has yet operated in the terminal state.
Chains that copied it, and one that gave up on it
The mechanic travels easily. Litecoin's mainnet consensus parameters set a subsidy halving interval of 840,000 blocks, four times Bitcoin's count, matched to a faster block target so the cadence lands in a similar place.2 Copying an interval is a one line change. Inheriting the terminal state is the decision that actually gets made.
Dogecoin is the instructive counterexample, because it changed its mind. Its rewards originally halved every 100,000 blocks, following the same pattern. From block 600,000 the schedule was replaced with a permanent reward of 10,000 DOGE per block, so issuance never stops and the supply has no cap.3 A chain that copied the halving decided, several steps in, that it preferred a floor.
What we take from it when designing a schedule
Three things. A step cut is defensible when it is computable years ahead, applied uniformly, and denominated against a market deep enough to reprice around it, which is the condition Bitcoin's halving meets and most emission cliffs do not. A terminal state of zero is a commitment to a fee market you do not yet have evidence for, so it needs an explicit answer to the Carlsten result rather than silence. And a schedule concentrating its issuance early is concentrating its security spend early, which suits a network whose value is meant to compound and suits very little else.
The token is the payment rail for that security spend. What makes the spend affordable over decades is demand for the block space underneath it, and no curve shape substitutes for that.
Common questions
What happens at a Bitcoin halving?
The block subsidy paid to miners is cut in half at a fixed block height. Bitcoin's started at 50 bitcoin per block and halves every 210,000 blocks, about once every four years.1 Nothing else in the protocol changes. New supply enters at half the previous rate, miner revenue per block falls by half in the same instant, and mining costs stay exactly where they were.
When is the next halving?
It happens at a block height, not a calendar date. The subsidy halves every 210,000 blocks, so the next one lands at the next multiple of 210,000 above the current height.1 Because block intervals vary around the ten minute target, any date you see is an extrapolation from recent block times rather than a scheduled event, and the estimate tightens as the height gets closer.
Why do blockchains have halvings?
A halving does two jobs at once. It caps total supply, because repeated halvings sum to a finite amount, and it front loads the security subsidy into the years when the network has no fee revenue to speak of. The bet embedded in the design is that fee demand grows fast enough to replace the subsidy before the subsidy runs out. That bet has not yet been tested.
What happens when the block reward reaches zero?
Transaction fees become the only payment for producing blocks. Bitcoin's rule entitles blocks below height 6,930,000 to a subsidy, and nothing above it.1 Whether fee-only mining is stable is contested: Carlsten and co-authors argue it produces intermittent mining, incentives to fork for rich blocks, and easier selfish mining.4 The alternative design, a permanent subsidy floor, is what tail emission does.
See Tokenomics Design Services for how this applies in practice.
Sources
- Bitcoin Developer Reference: Block Chain, block subsidy and halving
bitcoin.org / Bitcoin Core developer documentation, current
States that the block subsidy started at 50 bitcoins and is halved every 210,000 blocks, approximately once every four years, and that only blocks below height 6,930,000 are entitled to a subsidy. - Litecoin Core consensus parameters (src/chainparams.cpp)
Litecoin Project, litecoin-project/litecoin repository, current
Mainnet consensus block sets consensus.nSubsidyHalvingInterval to 840000, four times Bitcoin's interval. - Dogecoin Core Frequently Asked Questions, block reward schedule
Dogecoin Core developers, dogecoin/dogecoin repository, current
States that rewards halve every 100,000 blocks and that from block 600,000 a permanent reward of 10,000 Dogecoin per block is issued, with the interval-by-interval reward table. - On the Instability of Bitcoin Without the Block Reward
Carlsten, Kalodner, Weinberg and Narayanan, ACM CCS 2016 (author copy, Princeton University), 2016
Formal analysis of mining incentives under transaction fees alone, finding intermittent mining, forking to capture high-fee blocks, and selfish mining profitable at lower thresholds.
Last reviewed 2026-08
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