A margin requirement is computed while trading. The margin requirement may be calculated while trading because the preferred system takes into account working orders to generate the margin requirement. The on the fly possibility allows the preferred system to provide pre-trade risk calculations, but can also be used to provide post-trade calculations. A generic spread number and the maximum number of outright positions are determined. Average expirations for the generic spread are computed. Using the spread positions, the average expirations and the maximum number of outright positions, a spread margin and an outright margin are calculated, which when summed provide a total margin requirement. Limits based in part on the total margin requirement may be imposed on one or more traders.