Bitcoin Stock-to-Flow (S2F) Model: How It Works & Its Limits

The Stock-to-Flow (S2F) model is a quantitative framework that measures an asset's scarcity by comparing its existing supply (stock) to its annual production rate (flow). The formula is simple:

S2F Ratio = Stock ÷ Flow

A higher S2F ratio means an asset is harder to inflate — it would take longer for new supply to significantly dilute existing holdings. This concept has been used for decades to analyze precious metals like gold and silver, where scarcity is a primary driver of value.

The model was adapted for Bitcoin by pseudonymous analyst PlanB in 2019, who published the original model on Medium. PlanB argued that Bitcoin's mathematically guaranteed supply schedule makes it uniquely suited for S2F analysis. Unlike gold, where mining companies can theoretically increase production when prices rise, Bitcoin's halving mechanism ensures that new supply decreases predictably every four years regardless of price.

This programmatic scarcity — combined with increasing adoption — forms the theoretical basis for S2F price predictions.

PlanB's Stock-to-Flow price model goes beyond just calculating the ratio — it uses regression analysis to derive price targets based on scarcity. The core formula is:

ln(Market Value) = a × ln(S2F) + b

Or in simpler terms: Price = e^(a × ln(S2F) + b)

Model Evolution:

S2F (Original, 2019): Used only Bitcoin's data points at monthly intervals. Predicted ~$55,000 after the 2020 halving.

S2FX (Cross-Asset, 2020): Incorporated gold and silver data points, arguing Bitcoin transitions through "phases" (Proof of Concept → E-money → Digital Gold). Predicted higher targets of $100K-288K by end of 2021 cycle.

Calculating the S2F Ratio Over Time:

Notice how each halving approximately doubles the S2F ratio, which the model interprets as fundamentally increasing Bitcoin's value floor.

Comparing S2F ratios across assets reveals why Bitcoin is often called "digital gold" — and why some argue it may become even more valuable:

Key Insights:

• Bitcoin now exceeds gold's S2F ratio — after the 2024 halving, Bitcoin is mathematically the scarcest asset by this metric
• Gold's S2F has been stable for millennia — mining output increases slowly and roughly matches jewelry/industrial demand
• Bitcoin's S2F will keep increasing — each halving doubles the ratio while gold's remains roughly constant
• Silver's lower S2F explains why it has underperformed gold as a monetary asset over centuries

The S2F Hypothesis: If markets value scarcity consistently across assets, and if Bitcoin achieves similar market acceptance as gold ($12-15 trillion market cap), then Bitcoin's price should converge toward valuations implied by its S2F ratio.

At gold parity (~$12T market cap), Bitcoin would be worth approximately $600,000 per BTC. S2F proponents argue this is inevitable; critics argue the model is oversimplified.

Explore the historical scarcity relationship with our On-Chain Metrics dashboard.

PlanB is the pseudonymous Dutch institutional investor who popularized the Bitcoin Stock-to-Flow model in March 2019. His analysis gained widespread attention for correctly predicting Bitcoin's general price trajectory through 2021.

Key Predictions Made:

• March 2019: PlanB predicted Bitcoin would reach ~$55,000 after the 2020 halving based on the original S2F model
• April 2020: S2FX (cross-asset) model predicted $100,000-288,000 by end of 2021
• Floor Model: PlanB later created a "worst case" floor model that predicted monthly price minimums

Results:

✅ Bitcoin reached $69,000 in November 2021 — exceeding the original S2F prediction of $55K

❌ Bitcoin never reached $100,000 in the 2021 cycle — falling short of S2FX predictions

❌ Bitcoin fell to $15,500 in 2022 — breaking the floor model's predictions for over a year

S2F Price Implications for Current Cycle (2024-2028): With S2F ratio of ~118, the model suggests fair value in the $100,000-200,000 range. However, the model's reliability for precise price targets has been questioned after the 2022 breakdown.

The April 2024 halving reduced Bitcoin's block reward from 6.25 to 3.125 BTC, pushing the S2F ratio to approximately 118 — nearly double gold's ratio. This milestone has important implications:

Historical Post-Halving Performance:

S2F Model Expectations: Based on the S2F ratio of 118, the model suggests Bitcoin's "fair value" in the $150,000-250,000 range by the end of this cycle. However, the model's track record on specific price targets has been mixed.

Monitor halving effects with our Halving Countdown and track supply metrics with our Supply Calculator.

The Stock-to-Flow model has faced significant criticism from economists, traders, and even other Bitcoin analysts. Understanding these critiques is essential for using the model appropriately:

Fundamental Criticisms:

• Demand is ignored: S2F only models supply scarcity, but price is determined by supply AND demand. A scarce asset with no demand is worthless.
• Circular logic: The model assumes scarcity → value, but this relationship is not automatic for digital assets
• No comparable assets: Gold took thousands of years to develop its S2F-price relationship; applying it to a 17-year-old asset may be premature
• Cannot go to infinity: The model implies exponentially increasing prices forever, which is mathematically impossible

Statistical Criticisms:

• Cointegration issues: Time series data for both S2F and price are non-stationary, making regression potentially spurious
• Overfitting: The model was fit to limited historical data and may not generalize to future conditions
• Model selection bias: Other models (like the Power Law) show similar or better fits with different theoretical foundations

Practical Failures:

• 2022 breakdown: Bitcoin spent over 12 months below S2F model predictions, with actual price 75% below "fair value"
• Floor model invalidated: PlanB's floor model was violated for extended periods
• S2FX overestimation: The cross-asset model predicted $100K+ by end of 2021, which didn't materialize

Defenders' Response:

• S2F is a long-term model; short-term deviations are expected
• External shocks (Fed policy, FTX collapse) caused temporary dislocations
• The model correctly identified the general direction over multiple cycles
• No model is perfect; S2F provides a useful framework for thinking about scarcity

Best Practice:

The S2F model's value lies in conceptual understanding of scarcity rather than exact price forecasts.