A computer trading system for determining a calculated value for a user defined contract on a future characteristic(s) of a financial market comprises a receiving component for receiving a parameter(s) from a user defining the user defined contract and receiving financial market data concerning the financial market. The system includes a calculating component operable to determine a calculated value, such as a price, payout, or odds, for the user defined contract based on the parameter(s) and the financial market data and a transmission component for transmitting the calculated value to the user. The receiving component may also receive an order for the user defined contract from the user based on the calculated value to thereby create an obligation for a bookmaker to pay a payout amount upon the occurrence of the future characteristic(s) of the financial market satisfying the parameter(s).