Stock-to-Flow, explained

Formula

Stock ÷ Flow

existing supply over annual issuance

Risk factor weights

45/25/20/10

price position / momentum / volatility / halving

Heatmeter weight

4%

one of 14 inputs, both Bitcoin & Ethereum

Next halving

~2028

reward falls to 1.5625 BTC (estimated)

A scarcity-based valuation model for Bitcoin, popularized by the pseudonymous analyst PlanB in 2019. It divides existing circulating supply (the stock) by how much new supply enters the market per year (the flow). The higher the ratio, the smaller new issuance is relative to everything already mined — and unlike gold or silver, Bitcoin's flow drops on a fixed, publicly known schedule: roughly every four years, the block reward — and with it, new issuance — is cut in half.

That halving schedule is what makes the model tempting: it turns Bitcoin's supply side into a predictable staircase, and PlanB's original contribution was fitting a formula to past data that translated each step of that staircase into an implied market cap.

We don't count circulating supply on the chain directly. Instead we follow the issuance schedule forward from the date of Bitcoin's first block, in 210,000-block halving eras at an assumed 144 blocks per day, adding up the reward earned in each era until it reaches the date in question — capped at the 21,000,000 BTC hard cap. Annual issuance is simpler: the current era's block reward times 52,500 (an approximation of blocks mined per year). S2F is then just stock divided by flow: supply ÷ annual issuance.

Price history comes from CoinGecko, extended back with early 2010-era Bitcoin prices from before CoinGecko's own coverage begins, and plotted weekly.

Once we have the S2F ratio for a given date, the model price comes from the formula PlanB fitted in 2019: market cap = e^14.6 × S2F^3.3, divided by circulating supply to turn a market cap into a price per coin. Both numbers — 14.6 and 3.3 — are PlanB's own, the values he arrived at by fitting the formula to Bitcoin's historical market cap against its historical S2F ratio. We do not re-fit or update them; we apply the original published values exactly as they were.

The percentage gap between that model price and the actual price is the figure the chart calls the deviation. It's the number the model is famous for — and, as the next section explains, it is not the number that drives this page's risk score.

One thing to be clear about: the risk score on this page is not a measure of how far price has strayed from the S2F model price. It's a separate weighted blend of four factors that describe recent price behaviour, not scarcity valuation:

Cycle price position (45%) — where the current price sits within its own trailing 2-year range, from 0 (at the low) to 100 (at the high). Momentum (25%) — how fast price has moved over the last 30 periods, mapped onto a curve. Volatility (20%) — how widely price has swung over that same 30-period window. Halving cycle position (10%) — how far the current date sits within the four-year cycle since the last halving, scored on a curve that peaks around the three-quarter mark.

Those four scores are combined into a raw weighted average, then stretched to fill the full 0-100 range using the lowest and highest raw scores seen across the whole history (plus a small buffer either side), because a straight weighted average of these four factors rarely reaches the true extremes on its own.

Yes, and unusually clearly for a valuation model. PlanB's original 2019 model projected a price floor for Bitcoin that actual price fell well below during the 2021-2022 drawdown — a miss that is widely documented across the industry and is a large part of why this model remains one of the most argued-over in crypto, rather than a quietly accepted classic.

Stock-to-Flow measures scarcity with precision and predicts price with none. Our risk score doesn't pretend otherwise — it scores the price, not the model's claim about the price.

Watch the staircase for scarcity, the price line for everything else. The S2F ratio only moves at halvings — it's a fact about supply, not a forecast. The model price derived from it moves in step with that staircase. Actual price does whatever demand does, independent of either.

Don't read the 0-100 risk score as "how overvalued vs. the model." As section 04 covers, it's a price-behaviour score — cycle position, momentum, volatility, halving timing — that happens to live on this page. If you want the actual model-price gap, that's the separate deviation figure on the live chart, not the risk gauge.

Stock-to-Flow is a supply-side indicator — it describes Bitcoin's issuance schedule with certainty and says nothing about demand, which is exactly the gap that produced its most public miss. On this platform it also contributes a price-behaviour reading through its risk score, which is a different thing from the scarcity model it's named after.

It appears in both the Bitcoin and Ethereum Heatmeters, at a weight of 4 out of 100 in each. On the Ethereum Heatmeter it is one of seven inputs that stand in for Bitcoin — there is no separate Ethereum issuance-scarcity model behind it, so it carries Bitcoin's halving-driven signal into the Ethereum composite rather than measuring anything Ethereum-native. In neither heatmeter does it decide the score alone — it's one voice, at a modest weight, among fourteen.

Others in on-chain — What the blockchain itself says about holders, miners, and what people paid for their coins.

• Volume MomentumTrading volume against its own yearly baseline — speculative heat rather than price.
• AHR999Compares today’s price with what buyers have typically paid over the long run — built for spotting cheap stretches.
• Puell MultipleThe daily value of newly issued coins against its yearly average — miner revenue as a cycle signal.
• Cost of ProductionA modelled miner cost floor from difficulty and issuance, and how far price trades above it.
• RHODL RatioThe balance between recently moved coins and long-dormant ones, which peaks near cycle tops.

Every indicator we track — the full glossary.