The disposition effect has been characterized in various ways: the “effect, whereby investors are anxious to sell their winners, but reluctant to sell their losers” (, pp. 419); “the tendency to hold losers too long and sell winners too soon” (, pp. 1775) and the effect, whereby investors “sell winners more readily than losers” (, pp. 1779). The most discernable aspect of these characterizations is their imprecision, particularly with regard to time. In what follows, we provide a detailed explanation of the disposition effect based on a straightforward application of prospect theory (Kahneman and Tversky [1992]; Kahneman and Tversky [, ]). The analysis begins with the traditional account of the disposition effect and provides precise time-independent concepts that replace “sell too soon” and “hold too long.” The analysis shows when the prospect theory explanation of the disposition effect requires only the valuation function and when the explanation requires both the valuation function and the probability weighting function.