Imagine a metal accumulated over a long history, with mines adding only a small fraction each year. Stock-to-Flow compares these two things: the existing stock and the pace of new production. It helps explain the size of new additions relative to what already exists. For Bitcoin, the inputs are issued coins and new coins created through mining. The ratio does not tell you what people will pay for them. To forecast a price, we need to build and test a price model. A high ratio alone does not guarantee a rising price.
CFA Institute, an organisation that educates investment professionals, distinguishes the stock, S, from annual new production, F. Try our simple example: 1 000 units already exist and 50 are added each year. S/F is 20 years. At an unchanged pace, producing an amount equal to today’s stock would take that long. It does not mean the stock runs out in 20 years, must be consumed, or that the result is a price. This measures the pace of additions, not a countdown to expiry. For the calculation to make sense, both quantities need compatible units and the flow needs a clearly specified period. [1]
BTC is the unit used for amounts of bitcoin. For Bitcoin, we can start with coins issued by a particular date. Our hypothetical stock of 20 000 000 BTC differs from the commonly stated 21 000 000 BTC limit discussed in 21 Million. That limit includes coins not yet created; it cannot automatically replace today’s stock in this calculation. Bitcoin.org also explains lost private keys, the secret data a wallet uses to sign payments: coins remain recorded, but their owner may no longer be able to spend them. Subtracting them requires an estimate and an explanation of the method. A long-inactive address alone does not prove lost keys. Our number is illustrative, not a current measurement. [7]
Bitcoin Core v30.0 is a version of software that checks bitcoin payments and blocks: batches of payments added to the network’s shared record. Its mainnet code reduces the subsidy every 210 000 blocks and sets a target block interval of 600 seconds. Block Subsidy is this newly created part of the reward. Assuming miners claim the full subsidy of 3.125 BTC and there are 144 blocks a day for 365 days, the annualised flow is 164 250 BTC. The actual number of blocks in a calendar year can differ. A miner also receives transaction fees, but these transfer existing coins. Only the subsidy is new production. Treating the miner’s entire income as issuance would therefore inflate the flow we want to measure. [3] [2]
Halving, the subsidy being cut in half, reduces the pace of new issuance. Hold our hypothetical stock fixed at 20 000 000 BTC: annual flow of 328 500 gives 60.88 years, while flow of 164 250 gives 121.77 years. This is a doubling of the ratio, not an instruction to double the price. If the measured year contains exactly half its time at the old rate and half at the new rate, hypothetical flow is 246 375 and the ratio 81.18. A trailing-year total can therefore differ from annualising the rate in force today. Before comparing charts, establish which version they show. [2]
Imagine a positive stock and flow F = 0. S/F is then undefined, because division by zero is not defined. But the ratio growing as flow approaches zero does not mean a buyer offers an infinite price. Bitcoin Core calculates the subsidy in whole satoshi, the smallest units of bitcoin, so repeated halvings eventually end new subsidy issuance. Fees can continue passing from users to miners. Zero new issuance is not the same as zero reward and says nothing by itself about existing coins’ purchasing power. That remains a matter of actual demand and exchange. [2]
World Gold Council, an organisation focused on the gold market, separates above-ground gold, meaning gold already mined, from gold still in unmined deposits. It also distinguishes new mining from recycling. In our own hypothetical figures, above-ground stock of 200 000 tonnes and mining of 4 000 tonnes a year give a ratio of 50 years. Adding 1 000 tonnes of recycling to the flow produces 40. Yet melting down jewellery has not increased the total above-ground stock; the metal has changed form or owner. Recycling matters for market supply, but it is not newly mined gold. These are not current statistics. The example shows why comparisons require matching definitions of both stock and flow. [4] [5]
Store of Value means keeping purchasing power for the future: what your savings can buy. A high Stock-to-Flow can inform an argument about slow supply growth, but does not ensure that ability. CFA Institute therefore discusses the price model’s limitations too. The advanced expression log(P) = a + b × log(S/F) connects price P to the ratio using logarithms; a and b still have to be estimated from data. A logarithm helps handle widely differing magnitudes, but does not supply missing demand. The author must specify currency, period, and whether the estimate concerns price or the combined value of all coins. A close fit between historical curves does not establish causation; the same ratio can accompany rising or falling prices. [1]
Joseph Simonian, writing for CFA Institute Research Foundation, discusses overfitting: a model can describe the past beautifully precisely because we tailored it too closely to that past. He also warns against using information unavailable during the period being tested. Here is a practical check: estimate parameters using data through 2020, then test later data without retrospective selection based on the outcome. Examine errors, forecast horizon, and comparison with a simple estimate such as the last known price. Neither a neat historical curve nor a narrowly drawn band guarantees a future target. A ratio and a validated forecast remain different things. [6]
For the clearest picture, read this entry together with 21 Million, Halving, Block Subsidy, Store of Value, Bitcoin Core. The reverse links also lead from Saifedean Ammous, Stock-to-Flow Model, The Bitcoin Standard.