The the thing about backtesting a strategy is that it is very easy to make a mistake in your backtester. Look ahead bias is the most common mistake.
Another challenge is the data. Are you testing against a history of stocks that includes bankruptcies? If not you have survivorship bias.
I suggest you take a look at my website, www.quantopian.com. Look at our open-sourced backtester, https://github.com/quantopian/zipline. Between the two we can help you get past those two sources of error.
The the thing about backtesting a strategy is that it is very easy to make a mistake in your backtester. Look ahead bias is the most common mistake.
Another challenge is the data. Are you testing against a history of stocks that includes bankruptcies? If not you have survivorship bias.
I suggest you take a look at my website, www.quantopian.com. Look at our open-sourced backtester, https://github.com/quantopian/zipline. Between the two we can help you get past those two sources of error.