A method and system for providing downside protection of stock market investments. The present invention allows stock prices to be expressed as a stop loss percentage of the high value the stock price attains rather that a fixed or "hard entered" number. The stop loss percentage of the high value allows stock prices the freedom to increase in price while protecting gains that are being made and still providing downside protection for market declines. The system receives security information input from the user and also data link information of current stock information, the system determines new high values and calculates a sell threshold price based on the stop loss percentage and the high value of the security. When the market price is less than the sell threshold price, the system notifies the user or automatically sells the security.