Calibrating Harvestability

Starting from the canonical fin_harvestability object \(h(T,\tau)=1-e^{-T/\tau}\), this paper studies the calibration problem: when does expected return begin to dominate volatility strongly enough that the premium can be treated as genuinely available to the investor, and how should the time scale \(\tau\) be documented in practical use? The root derivation lives in the companion theory paper topics/fin_harvestability/paper.md; the role of the present paper is narrower. We derive \(\tau\) from two usable routes. Under Ornstein-Uhlenbeck dynamics, \(\tau\) is the mean-reversion half-life. Under a geometric Brownian motion approximation, \(\tau = \sigma^2/\pi^2 = 1/\text{Sharpe}^2\), where \(\pi\) is excess return and \(\sigma\) is volatility. The second route yields a simple calibration formula when full eigenmode estimation is unavailable. We document default \(\tau\) values for Cash, Bonds, Equity, and Alternatives, discuss empirical calibration from return series, and show how fin_harvestability enters lifecycle allocation and advisory methodology. The paper is therefore a calibration and application companion to the proof-first fin_harvestability root, not a replacement for that root theory paper.