Bitcoin’s halving is a change in the maximum new bitcoin that a block may create. Mainnet uses an interval of 210,000 blocks. The starting subsidy is 5,000,000,000 satoshis, or 50 BTC. Network parameters and subsidy code.
Calculate an era
Divide the block height by 210,000 and discard the remainder. That gives the subsidy era, starting at zero. The initial subsidy is then divided by two that many times, with the result rounded down to a whole satoshi. Bitcoin Core implements this using integer arithmetic. GetBlockSubsidy.
At height 210,000 the subsidy is 25 BTC. At 840,000 it is 3.125 BTC. At 1,050,000 it becomes 1.5625 BTC under the existing rules. These are statements about heights, not a prediction of which calendar day those heights will occur.
Supply, not price
Adding the scheduled subsidies gives an upper bound just below 21 million BTC. That does not equal the amount available to spend: the original genesis subsidy is unspendable, and coins may be lost or rewards underclaimed. Validation rules.
The supply formula says nothing by itself about future demand or a market price. This calculator deliberately shows only the rule it can compute.
Miners still collect fees
The subsidy is one component of a miner’s permitted reward. Transaction fees are separate. A reduction in subsidy does not guarantee a proportional reduction in total revenue, and it does not ensure that an operation remains profitable. Coinbase reward validation.
A height, not an appointment
The first halving block records a real event. Future block dates are estimates because arrivals are irregular. It is precise to say “at the next multiple of 210,000”; it is not precise to promise an exact future date.
A schedule written in blocks.
Move between eras to see the permitted subsidy at each starting height.
Subsidy only; excludes transaction fees. Uses whole-satoshi rounding. It does not estimate prices or activation dates.