Today is the day taxes are due in the U.S.  The reason tax day may be important is that it is the last day that people can make IRA contributions to count for the previous tax year.  This can create a last-minute rush and you will often have an inflow of funds heading into the market right around and on April 15th.  Fund managers will often put this money to work immediately and it creates a positive bias for the market.  Tax Day itself seems to have benefited over the years.  Below are some stats that demonstrate this.