Stock-to-flow calculator
PlanB's scarcity model. Popular, but increasingly broken post-2022.
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The Stock-to-Flow (S2F) model, popularized by PlanB in 2019, predicts Bitcoin price based on the ratio of existing supply (stock) to new supply per year (flow). Higher S2F = scarcer asset = higher predicted price. The model fit historical data well through 2020-2021 but has been off by 50-70% since late 2021.
This calculator runs the S2F formula with your chosen coefficient. Use it for historical context, not as a forward price oracle — the model's authors themselves have acknowledged its predictive failure post-2021.
The original S2F formula: market cap = exp(14.6) × S2F^3.3, derived by log-log regression on BTC price history from 2009-2019. It predicted a $100K BTC after the May 2020 halving (close enough — BTC hit $69K in November 2021) and a $288K BTC after the April 2024 halving (BTC reached roughly $100K as of 2025, a 65% miss). The predictive gap has widened with each cycle.
Gold has a stock-to-flow ratio of roughly 60-70 (60-70 years of existing supply vs annual mining). Silver sits around 20. After the 2024 halving, Bitcoin's S2F is approximately 120 — twice as scarce by this measure as gold. The model argues that scarcity alone justifies a price multiples higher than gold. The problem is that demand for gold comes from millennia of monetary history; Bitcoin's demand is newer and driven by narratives that can change faster than mining schedules.
Current S2F output (post-April-2024 halving)
Existing BTC stock: ~19.7M coins.
Annual new flow (post-halving): ~164,000 BTC/year (450/day × 365).
S2F ratio: 19.7M / 164K = 120.
S2F model formula (PlanB original): price = 0.4 × S2F^3 ≈ $692,000.
Actual BTC price (2025): ~$65-95K range.
Model error: 80%+ overshoot.
Why S2F broke (probably)
Several reasons: (1) Bitcoin's market cap is now large enough ($1T+) that it correlates with macro liquidity more than native supply dynamics; (2) the model was always a curve-fit on 3-4 data points (prior halvings) and was bound to break with larger N; (3) demand dynamics (ETF approval, sovereign adoption) aren't in the model at all. S2F assumed scarcity alone drives price; reality is scarcity + demand + liquidity + narrative.
What the S2F ratio actually measures — and doesn't
S2F measures supply-side scarcity: how many years of current production it would take to double the existing supply. For BTC at S2F = 120, it would take 120 years of current mining output to produce as much BTC as already exists. This is a meaningful number. What it does not measure: demand, utility, regulatory environment, competing assets, or the willingness of existing holders to sell.
Precious metal comparisons are the model's strongest justification. Gold's price relative to its S2F (roughly $60K per unit of S2F at $3,800/oz and S2F~60) has been relatively stable over decades. If BTC reaches the same ratio: S2F = 120 × $60K/S2F-unit = $7.2M per BTC. That math requires accepting that BTC achieves gold's monetary status — a big assumption. If BTC achieves silver's status instead, the implied price is far lower.
The model also ignores lost coins. Chainalysis estimates 3-4 million BTC are permanently inaccessible (lost keys, Satoshi's dormant wallets, early mining losses). The true liquid supply is closer to 15-16 million coins, not 19.7 million. Using the illiquid-adjusted stock raises the true S2F above 140, which increases the theoretical model output. This partially explains the gap; the model was calibrated on total supply, not liquid supply.
Alternative scarcity metrics worth knowing
The Puell Multiple measures miner revenue relative to its 365-day average. It captures whether miners are generating above-average income and are thus incentivized to sell. Puell > 4 has historically coincided with cycle tops (overpaid miners sell); Puell < 0.5 has marked cycle bottoms (underpaid miners capitulate). It is a better real-time indicator than S2F because it uses actual miner behavior, not theoretical scarcity.
Thermocap ratio compares market cap to cumulative miner revenue. Miners are the only consistent sellers in the Bitcoin ecosystem — they must sell to cover operational costs. When market cap is 50x+ cumulative thermocap, speculation dominates; when it is below 20x, longer-term holders dominate. This metric avoids the demand-side blindness of S2F and has been more consistent in identifying cycle phases.
Realized cap and MVRV remain the most reliable on-chain frameworks. Realized cap (sum of BTC at price last moved) tracks actual holder cost basis. When market cap is 5-7x realized cap (MVRV 5-7x), everyone is deeply in profit and selling pressure is extreme. These ratios have topped within 10-15% of every historical cycle peak. No forward price target, but more honest about what the data can and cannot tell you.
How to use S2F in an actual investment framework
Use S2F as a floor check, not a price target. If BTC is trading significantly below the S2F implied price, scarcity is underpriced — bullish signal. If BTC is trading significantly above S2F implied price, something besides scarcity is driving the move — more cautious signal. The model does not tell you when to buy or sell; it contextualizes where current price sits relative to a supply-based anchor.
Combine with macro cycle awareness. S2F failed post-2021 partly because the Fed started the fastest rate-hiking cycle in 40 years (2022-2023), pulling capital out of risk assets including BTC. The model has no macro variable. A simple overlay: if S2F says $500K but real rates are at 5%, treat the prediction with extreme skepticism. If S2F says $300K and real rates are at 0% or negative, it deserves more weight.
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Stock-to-flow — frequently asked questions
Who created the Stock-to-Flow model?
A Dutch institutional investor known as 'PlanB' (pseudonymous, later revealed as Marc-Paul Burger in some interviews). Published the original paper 'Modeling Bitcoin's Value with Scarcity' on Medium in March 2019. The model gained massive popularity during the 2020-2021 bull run when predictions were tracking closely.
What's the current S2F target?
Using PlanB's original formula and current S2F: ~$600-700K BTC. Using the revised 'S2FX' (S2F-Extended) formula that includes 'phase transitions': $1M+. Both are significantly above current price. The gap is either (a) the model is wrong or (b) we're early in a new cycle; popular consensus has shifted toward (a).
Is S2F a scientific model?
Not really. It's a curve-fit on historical data with one primary variable (supply scarcity). Real financial modeling requires out-of-sample validation, control for confounding variables, and statistical significance testing — S2F doesn't meet any of those standards. It was useful as a narrative vehicle more than a predictive tool.
Are there better BTC price models?
Several alternatives have better out-of-sample track records: (1) NVT ratio (network value to transactions) for valuation; (2) MVRV (market value to realized value) for cycle-position; (3) Mayer Multiple (price vs 200-day MA) for momentum; (4) Pi Cycle Top Indicator for cycle-top timing. None are perfect; using a combination is more robust than any single model.
Will S2F work again?
Depends on what you mean. If you mean 'will BTC follow S2F's predictions?' — probably not going forward, because demand dynamics dominate. If you mean 'will scarcity continue to matter for BTC?' — yes, halvings continue to reduce new supply, and that structurally supports long-term price. The narrative force of scarcity is real; the quantitative precision of S2F is broken.
What does S2F say about gold and silver?
Gold's S2F is roughly 60-70 (existing surface stock divided by annual mining). Silver is around 20-22. By S2F logic, gold's higher scarcity ratio is why it commands a higher price per unit than silver. Bitcoin at S2F = 120 post-halving is twice as scarce as gold by this measure. Whether the market eventually prices it that way depends on adoption as a monetary asset — which is a demand argument, not a supply one.
Has any other asset validated the S2F relationship?
PlanB applied S2F to gold and silver as supporting evidence, showing both fit the same power-law curve as BTC. The problem is three data points (BTC, gold, silver) do not validate a model. Other commodities like oil, wheat, and copper have high flow relative to stock and low prices — consistent with S2F directionally but not the same power law. The model works within the 'hard money' asset class but should not be extrapolated beyond it.
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