Stock index futures added to losses on Friday after data showed U.S. economic growth slowed more than expected in the second quarter.

S&P 500 futures fell 9 points and 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 78 points and Nasdaq 100 futures lost 15.50 points.

(Reporting by Caroline Valetkevitch)