S&P 500 stock index futures turned negative on Tuesday after retailer Best Buy Co Inc said third quarter domestic sales were softer than expected and lowered its full-year outlook.

S&P 500 futures fell 0.3 points and were slightly 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 8 points, while Nasdaq 100 futures fell 2 points.

(Reporting by Edward Krudy; Editing by Padraic Cassidy)