U.S. stock index futures fell on Monday as investors fretted about the fallout from Japan's massive earthquake and tsunami.

S&P 500 futures lost 5.1 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures fell 33 points, and Nasdaq 100 futures dropped 13.50 points.