🔮 Bitcoin Stock-to-Flow (S2F) Calculator

S2F is the most controversial and most discussed Bitcoin price model in existence. I have followed PlanB since 2019, watched the model hit within 25% of its cycle target, then watched it miss spectacularly when S2FX predicted $288,000 for the 2020-21 cycle. Here is an honest assessment of what it gets right, what it gets wrong, and how to actually use it without deluding yourself.

What Stock-to-Flow Measures

Stock-to-Flow is a commodity scarcity model. "Stock" is the total existing supply of a commodity — all the Bitcoin ever mined that still exists. "Flow" is the annual new production — the new Bitcoin created by miners each year. Divide stock by flow and you get the S2F ratio: how many years it would take to double the existing supply at current production rates.

Bitcoin at S2F 120.9 is now approximately twice as scarce as gold by this metric. After the 5th halving in 2028 (block reward drops to 1.5625 BTC), the annual flow halves again, pushing Bitcoin's S2F ratio toward ~450 — entering mathematically uncharted territory for any asset in human history.

The S2F Model History

The Bitcoin S2F model was created by a pseudonymous Dutch investor and former institutional money manager known as PlanB (@100trillionUSD on X/Twitter) and published in March 2019 in a paper titled "Modeling Bitcoin Value with Scarcity." The original model applied regression analysis across Bitcoin's price history relative to its changing S2F ratio and found a remarkably tight correlation. The paper spread rapidly through the Bitcoin community and became one of the most-read analyses in the space. PlanB later extended it into the S2FX (cross-asset) model, which incorporated gold and silver data points to project $288,000 for the 2020-2024 cycle. The original S2F model was directionally correct: it predicted $55,000+ for the cycle, and BTC hit $68,789 in November 2021. The S2FX extension predicted $288,000 for that same cycle — a level BTC never reached.

How to Read the S2F Chart

The S2F chart plots model price versus actual price over time. The model price is the output of PlanB's formula — ln(price) = 3.31819 × ln(S2F) + 14.9 — which produces a smooth curve that steps up with each halving. The actual price oscillates wildly around this curve. When Bitcoin trades significantly below the model price, historically this has represented undervaluation by S2F metrics. When Bitcoin trades significantly above the model price (as in late 2017 and late 2021), this has indicated overvaluation and has often preceded corrections. The current S2F model price, calculated using the formula above with today's ratio of approximately 120.9, sits in the range shown in the calculator above. If Bitcoin is below that value, the model calls it undervalued. For the 2024-2028 cycle, S2F model targets range from $200,000 to $300,000 depending on which version of the model you use.

Criticism and Limitations — An Honest Take

S2F ignores the demand side of the equation entirely. Supply scarcity is a necessary condition for high value, but it is not sufficient — demand must exist for that scarcity to translate into price. The model cannot predict regulatory bans, exchange collapses, macro rate cycles, or shifts in institutional appetite. The self-fulfilling prophecy criticism has merit: many traders buy Bitcoin because the S2F model says it should be worth more, not because of independent demand analysis. This creates reflexivity that may inflate price toward model targets, then collapse when believers lose confidence. PlanB himself acknowledged after the 2022 miss that the model may need revision for future cycles. My honest take: S2F is a genuinely useful framework for understanding Bitcoin's monetary policy and thinking about scarcity-driven value. As a precise price prediction tool, treat its targets as one scenario in a range of possibilities, not as a certainty.