Stock-to-Flow did something almost no other Bitcoin price model does: it named a specific price, for a specific date, and let the market prove it wrong. The model treated price as a function of the ratio between existing supply and new annual production, and its original version predicted levels for the period after the 2020 halving that price never reached. That failure, unlike Rainbow Chart's or Power Law's, is cleanly documented rather than quietly absorbed — which is actually the model working the way falsifiable science is supposed to, just not in the direction its proponents wanted.
The formula
Stock-to-Flow (S2F) is a scarcity ratio: existing supply ("stock") divided by new annual production ("flow"). Bitcoin's flow drops sharply at each halving, so its S2F ratio roughly doubles every four years. The model's original proposal fit historical price against this ratio and extrapolated it forward, implying specific price targets for specific future dates.
Why it made a falsifiable claim (unlike Rainbow Chart)
Where Rainbow Chart and Power Law present a corridor of "plausible ranges," the original S2F model published dated, numeric price targets following the 2020 halving. That's a meaningfully stronger, more falsifiable claim — and it's exactly why its failure is so clearly documented, rather than ambiguous.
What actually happened
Price never reached the levels the original model implied for the post-2020-halving period. Rather than treating scarcity in isolation, the shortfall is broadly attributed to the model ignoring the demand side of the equation entirely — a model built purely from a fixed, known supply schedule says nothing about whether buyers show up to absorb that supply at any given price, which depends on macro conditions, regulatory environment, and competing assets that have nothing to do with Bitcoin's issuance schedule.
Why this site still includes it
S2F is instructive precisely because it failed in a documented, dated way — a cleaner lesson in curve-fitting risk than models whose bands simply get quietly redrawn. It's included here as a historical case study in what a real out-of-sample failure looks like, with the original prediction and actual price both shown, not hidden.