Ten thousand dollars sits in the account. Risking a fixed portion of equity involves a different math than using total buying power, as the notes at orb trading sizing niacki detail. Every intraday trade requires a calculation of position size based on the distance between entry and stop. A mistake in the sizing of a position leads to uneven volatility exposure.
The Math of Equity Sizing
Equity sizing relies on the total liquidation value of the account. If the account holds ten thousand dollars, a one percent risk rule dictates a one hundred dollar loss limit. This calculation remains constant regardless of whether the broker provides margin. The distance from the entry to the stop loss determines the number of shares. A trade based on the opening range breakout uses this fixed equity number to maintain a consistent risk profile. Using this method keeps the drawdown predictable across every session. The math does not change when the market open approaches or when volatility spikes. Each trade is a discrete unit of risk tied to the net worth of the account.
The Mechanics of Buying Power
Buying power sizing uses the total margin available to the trader. This number is often much larger than the actual cash on hand. A trader might see fifty thousand dollars in buying power on a ten thousand dollar account. Sizing based on this number ignores the volatility of the underlying asset. A trade taken at the cash open using a percentage of buying power can result in a much larger dollar loss than a percentage of equity would allow. This method treats the margin as if it were part of the core capital. It creates a situation where a single bad move during the first hour can wipe out a significant portion of the actual cash. The leverage scales the risk beyond the actual equity levels.
Comparing Risk Profiles
The difference between these two methods shows up in the heat of a trade. Equity sizing scales the trade to the size of the account. Buying power sizing scales the trade to the size of the leverage. If a trader uses the thirty minute range to set a stop, the equity method will produce a specific share count. The buying power method will produce a much larger share count. This larger size increases the impact of the stop being hit. One method protects the principal. The other method maximizes the use of available capital. The choice dictates how the account reacts to a string of losses.
Execution and Timeframes
The timeframe used for the setup dictates the stop distance. A trade based on the 15 minute range requires a different share count than a trade based on the 60 minute range. When the stop is tight, buying power sizing allows for massive position sizes. When the stop is wide, equity sizing keeps the dollar risk the same. The math stays mechanical. There is no room for guesswork during the regular trading hours. The calculation happens before the order is sent. A small error in the calculation of the stop distance ruins the entire model.