Imagine two traders, same account, same entry signal. Trader A puts $50,000 into a single crude oil position. It gaps down 8% overnight. That's $4,000 gone — 8% of a $50,000 account wiped in one trade. Trader B, using fixed fractional sizing at 1% risk per trade, loses $500 on the same move. One sleeps fine. One does not.
The original Turtle Traders — trained by Richard Dennis in 1983 — were handed a complete system. The position sizing rules were not optional decoration. They were the load-bearing wall. Dennis understood that without mathematically defined sizing, even a statistically positive system destroys accounts through variance alone.
The Turtle method calculated position size using N, their term for Average True Range. One unit equalled 1% of account equity divided by N multiplied by the dollar value per point. On a $100,000 account risking 1%, if N on a futures contract equals $800 per contract, the position size is $1,000 ÷ $800 = 1.25 units, rounded down to 1 contract. Volatility drives size — always.
The Turtles also applied unit limits — maximum 4 units per market, 6 per correlated sector, 10 per direction (long or short) across all markets. This capped concentration risk mechanically. No discretion, no override. A trader wanting to understand the full mathematical architecture behind this approach can study fixed fractional position sizing, the original Turtle trading programme, and the role of Average True Range in volatility measurement to build an implementable framework.
The maths doesn't care about conviction. Size correctly, and a losing streak becomes a setback. Size incorrectly, and it becomes a funeral.
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