There are two big reasons that today is the best day for you to invest:

  1. The power of compound interest coupled with a long time horizon means you always want to start earlier than later -- and that means today. 
  2. Today, the market is undeniably cheap compared to its historical norms.

While it's impossible to predict the market's day-to-day movement, and it may well go down tomorrow, it could just as easily go up. Fortunately, at these prices, investors have more of a safety net built in than they can normally expect. 

One of the reasons the market is so cheap today is that big sectors like finance and energy are trading at deep discounts compared to their typical valuations.