Bitcoin Stock to Flow explained – ratio, calculation and limits

Bitcoin’s Stock‑to‑Flow (S2F) ratio stands at 116.7, derived from roughly 19.17 million BTC already mined versus an annual inflow of 191,250 BTC [1]. This high ratio signals extreme scarcity and underpins the model that links Bitcoin’s price to its limited supply.

How the ratio is built

The S2F metric divides the total existing supply (“stock”) by the yearly creation of new units (“flow”). For Bitcoin, the stock equals the cumulative mined coins, currently just over 19.2 million out of a 21‑million cap [1]. Flow is calculated from the block reward of 3.125 BTC every 10 minutes, which translates to about 191,250 new BTC each year. The resulting ratio of 116.7 is far higher than gold’s 62.3, implying that Bitcoin would need roughly 117 years of mining to double its existing supply [1].

Track record and criticism

Proponents cite a strong historical correlation: from 2015 through the end of 2021, the S2F curve tracked Bitcoin’s price rise, even as the asset hit an all‑time high of $69,000 in November 2021 [1]. However, the model missed price movements in 2011, 2013, and after the 2021 peak, when Bitcoin fell sharply and diverged from the S2F line [1]. Critics point to the model’s simplicity—it only considers stock and flow, ignoring market sentiment, macro news, and sudden shocks such as the “black‑Wednesday” crash on 19 May 2021 [2]. The model also failed to predict the 2022 price ceiling, overestimating a $100,000 target [1].

Forecasts derived from S2F

Plan B, the analyst who popularized the model, projected Bitcoin could surpass $100,000 by the end of 2021 and reach $1 million by 2025 [2]. These forecasts assume the S2F ratio continues to rise as halving events halve the flow every four years, theoretically driving price up tenfold each cycle [2].

What to watch

• Next halving – scheduled for 2024, will cut the block reward from 6.25 BTC to 3.125 BTC, reducing annual flow and pushing the S2F ratio higher.
• Price testing of $69,000 – the 2021 peak remains a psychological barrier; a breach could reinforce the model’s relevance.
• On‑chain supply metrics – monitor the proportion of BTC held by the top 1 % of addresses; concentration shifts can affect price dynamics independent of S2F.

The S2F ratio offers a clear, scarcity‑focused lens on Bitcoin’s valuation, yet its predictive power is limited by the model’s narrow focus and the market’s volatility. Whether future halvings will restore its historical alignment remains an open question.