What is the Bitcoin Security Index (BSI)?
The BSI is annualised miner revenue over market capitalisation: what Bitcoin pays for its own security, as a share of what that security protects. As of 2026-09-07 it is 0.82%.
Why a ratio rather than a dollar figure
A dollar figure moves with price and tells you nothing about whether it is enough. The ratio is scale-free: it asks what fraction of the protected value is spent protecting it. It is also the form in which the published opinions are stated, which makes them comparable.
What it is today, and what it becomes
| When | BSI | What changes |
|---|---|---|
| Today (2026-09-07) | 0.82% | subsidy 3.125 BTC/block plus fees at 0.64% |
| After ~April 2028 | 0.41% | subsidy halves to 1.5625 BTC/block |
| After ~2032 | 0.21% | halves again |
| After ~2036 | 0.11% | halves again |
Those forward figures hold the fee component flat and halve the subsidy on schedule. No price assumption enters. Price sits in both the numerator, through revenue, and the denominator, through market cap, so it cancels. A higher bitcoin price does not raise the ratio.
What counts as enough
Nobody has derived a floor from an attack model. Lyn Alden puts a healthy spend at 0.5%–1.5% of market cap a year. James McAvity put it at 1–1.5% in October 2023. Hasu defined the ratio in these terms in 2020, measured it at 2% at the time, and explicitly declined to name a floor. The 1% used across these pages is a round heuristic inside that spread, not a threshold.
Three bases
| Basis | Ratio | Gap / yr | Market cap to cover it |
|---|---|---|---|
| Trailing-year revenue over spot market cap | 0.92% | $1.27B | $24.40B |
| Trailing-year revenue over average market cap | 0.86% | $2.13B | $40.93B |
| Spot run-rate revenue over spot market cap (published) | 0.82% | $2.77B | $53.28B |
Three ways to measure the same ratio, all published. None of the three closes the gap.