When to sell

According to USA Today, you should sell a stock if it falls 10% or more from what you paid. Investors understand that it's difficult to get back to even after a loss greater than 10%. 

According to IBD founder William O'Neil, you should sell a stock when you are down 7% or 8% from your purchase price. This rule can help prevent an emotional decision to hang on too long. 

The SEC recently adopted Rule 201, which bans short selling if a stock has fallen more than 10% in a single day. 

A market correction is defined as a drop of less than 20%. A market crash is usually defined as a rapid market drop of more than 20%.