Few Bitcoin models have generated as much excitement, and as much heated debate, as Stock-to-Flow. For a while it looked almost prophetic, a tidy equation that linked Bitcoin’s scarcity to its price. Today it serves better as a cautionary tale about the difference between a compelling chart and a reliable forecast. It is worth understanding on both counts.
What stock-to-flow measures
Stock-to-flow (S2F) is a scarcity ratio borrowed from commodities. The “stock” is the total existing supply of an asset. The “flow” is the amount produced each year. Dividing one by the other gives the number of years of current production it would take to replace the entire existing stock. Gold has a very high S2F because annual mining adds only a tiny fraction to the enormous above-ground supply. Consumable commodities have low S2F, because production turns over quickly.
For Bitcoin, the stock is the roughly circulating supply and the flow is the new coins issued by miners each year. A high S2F means new issuance is small relative to what already exists, which is the technical definition of scarcity.
Why halvings make the model dramatic
Bitcoin’s issuance is cut in half roughly every four years at each halving. Because the flow term is the denominator, halving the flow roughly doubles the stock-to-flow ratio overnight. This step-change is what made S2F so visually striking: every four years, Bitcoin’s measured scarcity jumps to a new level, and historically those jumps have preceded major bull markets.
This is the appeal in a sentence. A predictable, code-enforced supply schedule produces a predictable scarcity curve, and scarcity, the argument goes, should map to value.
The original PlanB model
The pseudonymous analyst PlanB published the model in 2019, fitting a power-law relationship between Bitcoin’s S2F ratio and its market value. The resulting chart showed price tracking the rising S2F line with what looked like remarkable fidelity across years of data, and it produced eye-catching long-term price targets. For a period, the fit was good enough that S2F became one of the most cited frameworks in the entire space.
Its appeal was partly aesthetic and partly emotional. It gave a simple, deterministic story (scarcity goes up, price goes up) and a number to anchor to, which is exactly what many investors wanted during volatile cycles.
The criticisms, stated plainly
The model has serious problems, and being honest about them matters more than the original hype did.
- It has diverged from price. The post-2021 period saw price fall well below the trajectory the model implied, breaking the tight historical fit that made it famous.
- It ignores demand entirely. S2F is a pure supply model. Price is set by supply and demand together. A model with no demand variable cannot explain why scarcity would translate into any particular price, only that supply is tightening.
- It is statistically fragile. Critics have shown the strong fit relied heavily on a short, trending sample and on comparing two series that both rise over time, a setup prone to spurious correlation. Reasonable changes to the method weaken or break the relationship.
- It treats a forecast as destiny. Encoding a deterministic price path from supply alone implies markets must follow the schedule, which is not how price discovery works.
How to actually use it
None of this means scarcity is irrelevant. Bitcoin’s fixed, disinflationary issuance is genuinely unusual and worth understanding. The right move is to demote S2F from oracle to lens: one way to visualize the supply side, useful for framing the halving narrative, not for setting price targets.
Far more dependable are valuation tools grounded in real onchain cost basis and demand. The MVRV Z-Score measures how stretched price is versus the aggregate cost basis of holders, and has a strong record of flagging extremes. The Pi Cycle Top indicator uses moving-average behavior to highlight overheated conditions. And comparing realized cap with market cap grounds valuation in what holders actually paid rather than in a supply curve alone. These reflect demand and behavior, the variables S2F leaves out.
The bottom line
Stock-to-flow captures something real about Bitcoin’s scarcity and explains why halvings matter, but it is a supply-only model that has diverged from price, ignores demand, and rests on shaky statistics. Treat it as one scarcity lens among many, not a price forecast, and lean on demand-aware, cost-basis metrics when you actually want to judge valuation.
Common questions
What did stock-to-flow claim? That Bitcoin’s price could be modelled from its scarcity, expressed as existing supply divided by annual new issuance. Because issuance is known in advance, the model produced specific forward price levels.
Why did it break? Price diverged from the model by a wide margin and stayed there, which a model with predictive power should not do. The deeper problem is that it used a variable known years ahead to forecast one that is not, so it could never incorporate demand, regulation or liquidity.
Is scarcity therefore irrelevant? No. Supply issuance is real and matters. The error was treating a single supply variable as sufficient to determine price. The longer version is in why the stock-to-flow model broke.
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