U.S. stocks index futures added to losses on Wednesday after the ADP private employment report came in much weaker than expected in May and at its lowest level since September 2010, continuing a string of weak economic data.

S&P 500 futures shed 5.6 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 lost 43 points, and Nasdaq 100 futures fell 8.75 points.