Fidelity offers two ways to backtest strategies.

Single Symbol Backtesting

Use single symbol backtesting if you are interested in investing in a specific stock and want to see how it would have performed historically using a particular strategy.

Single symbol backtesting can help you identify trading opportunities but may not produce enough trade results to effectively evaluate the strategy.

Multi-Symbol Backtesting

Use multi-symbol backtesting to see how a group of stocks (such as the NASDAQ 100) would have performed historically using a particular strategy.

Multi-symbol backtesting enables you to create a more "real world" simulation since it includes the effects of dividends, cash interest, and commissions paid. It also allows you to choose a percent of equity to use for each trade based on the amount of trading capital selected. As the multi-symbol backtest is run, the system calculates gain/loss for each position, subtracts commissions, adds dividends or interest received, and adjusts the trade size up or down based on whether the system has a gain or loss at the particular time the trade signal for the next position is generated.

Because multi-symbol backtesting can more accurately reflect your trading style, you may be more successful in identifying an efficient trading strategy.

Used in combination, single symbol backtesting can help identify a trend or pattern that can then be validated over different time periods by using multi-symbol backtesting.