U.S. stock index futures briefly added to losses on Friday after government reports showed U.S. retail sales rose slightly less than expected in December, while overall consumer prices rose above forecasts.

S&P 500 futures fell 5.3 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 dropped 53 points, and Nasdaq 100 futures lost 2.25 points.

(Reporting by Chuck Mikolajczak)