U.S. stock index futures turned negative on Monday on worries about the strength of the economic recovery as companies, including Lowes Cos Inc posted muted outlooks despite strong results.

S&P 500 futures fell 1.2 points and were slightly above 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 dropped 13 points and Nasdaq 100 futures fell 2.75 points.