Over the years, day traders have developed many different ways to manage their money. Some of these are rooted in superstition, but most are based on different statistical probability theories. The underlying idea is that you should never place all of your money in a single trade, but rather put in an amount that is appropriate given the level of volatility. Otherwise, you risk losing everything too soon.

Calculating position size under many of these formulas is tricky stuff. That’s why brokerage firms and trading software packages often include money management calculators.

Optimal F is only one method. There are other methods out there, and none is suitable to all markets all the time. Folks trading both options and stocks may want to use one system for option trades and another for stock trades. If that’s your situation, you have one big money management decision to make before you begin: how much money to allocate to each market.

## Optimal F

The Optimal F system of money management was devised by Ralph Vince, and he’s written several books about this and other money management issues. The idea is that you determine the ideal fraction of your money to allocate per trade based on past performance. If your Optimal F is 18 percent, then each trade should be 18 percent of your account — no more, no less. The system is similar to the fixed fraction and fixed ratio methods, but with a few differences.

The following figure shows the equation for finding the number of shares of stock, N, to trade according to the Optimal F method.

The equation for finding the number of shares to trade under Optimal F

F is a factor based on the basis of historical data, and the risk is the biggest percentage loss that you experienced in the past. Using these numbers and the current price, you can find the contracts or shares you need to buy. If your account has \$25,000, your biggest loss was 40 percent, your F is determined to be 30 percent, and you’re looking at a stock trading at \$25 per share, then you should buy 750 shares:

An example of the Optimal F calculation

The Optimal F number itself is a mean based on historical trade results. The risk number is also based on past returns, and that’s one problem with this method: it only kicks in after you have some trade data. A second problem is that you need to set up a spreadsheet to calculate it (so read Ralph Vince’s book if you want to try it out).

Some traders only use Optimal F in certain market conditions, in part because the history changes each time a trade is made, and that history doesn’t always lead to usable numbers.