Trading Under A Tight Drawdown Mandate

Many trading mandates carry a hard stop: if the strategy's cumulative loss from its peak (the drawdown) hits some threshold — commonly 10% or 15% of capital — trading is paused or the book is unwound, no discretion allowed. This sounds like a rule that only matters once you're near the edge, but it actually reshapes behavior from day one, because a trader who gets shut down at −10% never gets to trade their way back to breakeven.

The key effect is asymmetric: losing 10% and being forced out is far worse than the raw dollar loss suggests, since it forfeits every future opportunity to recover. This pushes disciplined desks to size positions so that a run of bad luck — a few standard deviations of normal volatility, not even a true tail event — stays comfortably inside the mandate, leaving a buffer rather than sizing right up to the edge. A strategy expected to earn a solid Sharpe ratio can still be a bad idea under a tight mandate if its volatility means a plausible bad month would blow through the limit.

A simple sizing check: if a strategy's daily volatility is $\sigma$ and the mandate is a 10% drawdown, a rough rule of thumb is to size so that a 3-to-4 standard deviation cumulative move over the expected worst losing streak stays under the limit — leaving room for the drawdown to be measured from a peak, not from the starting capital, since it usually gets worse before the stop triggers.