What exactly is the 4 percent rule? It's a rule of thumb used to determine the amount of funds to withdraw from a retirement account each year.

The 4 percent rule seeks to provide a steady stream of money to the retiree, while also keeping an account balance that will allow those funds to be withdrawn throughout the person's retirement years. It's considered to be a "safe" rate, with the withdrawals consisting primarily of interest and dividends.

Read MoreWhy 4% retirement rule no longer works for most