Stock index futures added gains following data on retail sales and producer prices on Tuesday.

S&P 500 futures rose 13.2 points and were above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration of the contract. Dow Jones industrial average futures gained 67 points, and Nasdaq 100 futures added 20.25 points.

Total retail sales slipped 0.2 percent, falling for the first time in 11 months. Economists forecast a fall of 0.4 percent.

U.S. May producer prices rose 0.2 percent, more than expected.

(Reporting by Angela Moon)