The formula
Sharpe Ratio is a standard finance concept applied here to Bitcoin: it divides excess return (return above a risk-free rate) by the volatility taken to achieve it, over a chosen rolling window.
A higher Sharpe Ratio means more return was earned per unit of risk taken; a negative Sharpe Ratio means the asset lost money (net of the risk-free rate) over that window, regardless of how volatile it was getting there.
Why it's built from this site's own data
Rather than introducing a new external data feed, this site's Sharpe Ratio page combines the same 90-day annualized volatility already computed for the Volatility page with rolling return data — both already-verified quantities, reused rather than duplicated.
Why the historical range is so wide
Real historical Sharpe Ratio readings for Bitcoin have ranged from roughly -4.8 (during sharp drawdowns) to over +8.2 (during the fastest rallies) — an extremely wide band compared to traditional assets, where Sharpe Ratios rarely stray far outside roughly -2 to +3 even in extreme periods. That width is a direct consequence of Bitcoin's volatility being both larger and more variable than most asset classes, in both the numerator (returns) and denominator (volatility) of the ratio.
What a high Sharpe Ratio doesn't guarantee
A high trailing Sharpe Ratio describes a favorable risk-adjusted return over the specific window just measured — it says nothing about whether that combination of return and volatility will persist into the next window. Reading it as a forward guarantee is the same mistake as reading any trailing statistic as predictive.
Check where today's rolling 90-day reading falls against that real -4.8 to +8.2 historical range on the Sharpe Ratio chart.