Futures on U.S. stocks fell on concerns that the fiscal cliff might deteriorate the world's largest economy and on obscurity how Greece is going to repay the debt. Experts say the tax increases and spending cuts will come into force in January 2013, in case the Congress does not take an action. Contracts on Standard & Poor's 500 Index maturing December lost 0.7% to 1,368.1. Meanwhile, Dow Jones Industrial Average futures tumbled 0.6%.