Bitcoin Stock-to-Flow Model: Scarcity as a Valuation Framework
Alphractal Research · Sep 17, 2025 · 6 min read
The Stock-to-Flow (S2F) model is one of the most discussed and debated valuation frameworks in Bitcoin analysis. Popularized by the pseudonymous analyst PlanB in 2019, the model quantifies Bitcoin's scarcity by comparing the existing supply (stock) to the rate of new production (flow). While the model has generated significant controversy, understanding its mechanics and implications provides valuable context for any serious Bitcoin analyst.
What Is Stock-to-Flow?
The Stock-to-Flow ratio is a measure of scarcity borrowed from commodity analysis, where it has been applied to precious metals like gold and silver for decades.
Stock-to-Flow Ratio = Existing Supply (Stock) / Annual Production (Flow)
For Bitcoin:
- Stock: The total number of bitcoin in circulation (approximately 19.8 million as of early 2026)
- Flow: The number of new bitcoin mined per year (currently approximately 164,250 BTC annually at 3.125 BTC per block)
A higher S2F ratio indicates greater scarcity. The current Bitcoin S2F ratio is approximately 120, meaning it would take about 120 years of current production to replicate the existing supply. This places Bitcoin's scarcity above gold (S2F approximately 60) and far above silver (S2F approximately 22).
The Halving Mechanism
What makes Bitcoin's Stock-to-Flow uniquely interesting is the halving, a programmatic event that cuts the block subsidy in half approximately every four years (every 210,000 blocks).
Halving History and S2F Impact
| Event | Date | Block Subsidy | Approximate S2F | |-------|------|--------------|-----------------| | Launch | January 2009 | 50 BTC | ~1 | | 1st Halving | November 2012 | 25 BTC | ~10 | | 2nd Halving | July 2016 | 12.5 BTC | ~25 | | 3rd Halving | May 2020 | 6.25 BTC | ~56 | | 4th Halving | April 2024 | 3.125 BTC | ~120 |
Each halving doubles the S2F ratio by cutting the flow in half while the stock continues to grow (albeit at a decreasing rate). This creates a step-function increase in scarcity that is entirely predictable and immutable.
The S2F Price Model
PlanB's original model went beyond simply calculating the ratio. He proposed a log-linear relationship between S2F and market value, arguing that as Bitcoin's scarcity increases with each halving, its market value should increase proportionally.
The model regression suggested that Bitcoin's price should roughly follow a power law relationship with its S2F ratio. This produced price predictions that, for the first three halving cycles, tracked actual price performance with notable accuracy.
Key Model Predictions
The S2F model's accuracy through its first several cycles is what generated widespread attention:
- Post-2012 halving: Model suggested a price range that was broadly achieved during the 2013 bull run
- Post-2016 halving: The model's prediction aligned with the 2017 bull market peak
- Post-2020 halving: The model projected a six-figure price target, which Bitcoin approached but did not sustain in the 2021 cycle
Strengths of the S2F Framework
Quantifiable Scarcity
S2F provides a concrete, numerical measure of Bitcoin's scarcity rather than relying on qualitative arguments. The fact that each halving is predetermined allows analysts to model future scarcity with precision.
Cross-Asset Comparison
The S2F framework allows direct comparison between Bitcoin and other scarce assets. By placing Bitcoin on the same scarcity spectrum as gold and silver, it provides a framework for thinking about Bitcoin's potential market capitalization.
Supply Transparency
Unlike precious metals where production data is estimated and sometimes unreliable, Bitcoin's supply schedule is perfectly transparent and algorithmically enforced. This makes the S2F calculation for Bitcoin more precise than for any other asset.
Halving as Catalyst
The model provides a structural narrative for why Bitcoin's price tends to appreciate following halvings. Reduced supply issuance, combined with constant or growing demand, creates an economic imbalance that historically has resolved to the upside.
Criticisms and Limitations
The S2F model has faced substantial criticism from both within and outside the crypto community.
Demand Side Ignored
The most fundamental critique is that S2F is a supply-only model. Price is determined by the intersection of supply and demand, and the model treats demand as either constant or perfectly correlated with scarcity, neither of which is guaranteed.
Cointegration Concerns
Statisticians have raised concerns about the model's regression methodology, arguing that the apparent relationship between S2F and price may be a spurious correlation driven by two upward-trending variables rather than a genuine causal link.
Diminishing Returns
Each halving cycle has shown diminishing percentage returns. If this trend continues, the model's power law projection may overestimate future price performance.
Model Breaks
The S2F model predicted Bitcoin would sustain prices well above $100,000 during the 2021 cycle. While Bitcoin reached $69,000, it did not maintain the model's predicted range, leading to questions about the model's ongoing validity.
Infinite Value Problem
As halvings continue, the S2F ratio approaches infinity (when the block subsidy approaches zero). The model's log-linear relationship would imply an infinite price at infinite S2F, which is obviously unrealistic.
Using S2F in Context
Despite its limitations, the S2F framework remains a valuable tool when used appropriately.
As a Macro Framework, Not a Price Target
The S2F model is most useful as a broad framework for understanding Bitcoin's scarcity dynamics rather than as a precise price prediction tool. The general principle -- that increasing scarcity, all else being equal, should support higher valuations -- is economically sound.
Alongside Demand Metrics
On Alphractal, you can pair the S2F ratio with demand-side metrics to build a more complete picture:
- Active Addresses: Track network adoption and usage growth
- Exchange Inflows/Outflows: Monitor whether demand is materializing in actual accumulation
- Institutional Holdings: Track ETF flows and corporate treasury allocations
- NVT Ratio: Assess whether network value is supported by actual transaction throughput
For Halving Cycle Timing
The S2F model's most practical application may be in timing market entries relative to halving events. The pattern of pre-halving accumulation followed by post-halving appreciation has occurred consistently, even if the exact magnitude of each cycle's gains is unpredictable.
Alphractal's dashboard includes halving countdown timers and S2F overlays that allow you to track where Bitcoin sits in its current halving cycle relative to historical patterns. Alpha AI can provide analysis of how current S2F dynamics compare to equivalent points in previous cycles.
The Evolution of Scarcity Analysis
As Bitcoin matures, scarcity analysis is evolving beyond the original S2F model. More nuanced approaches consider:
- Effective supply: Accounting for lost coins and long-term dormant supply that effectively reduces the available stock
- Free float S2F: Only counting bitcoin that has moved recently, excluding dormant supply
- Demand-adjusted models: Incorporating demand-side variables alongside scarcity metrics
These refinements address many of the original model's shortcomings while preserving its core insight: Bitcoin's programmatic scarcity is a fundamental feature that distinguishes it from every other monetary asset in history.
Track Stock-to-Flow on Alphractal
Monitor Bitcoin's Stock-to-Flow ratio in real-time on Alphractal alongside 1,500+ other metrics. Alpha AI can provide contextual analysis of current readings and what they mean for your portfolio.
This analysis is for educational purposes only and does not constitute financial advice.