U.S. stock index futures fell further on Thursday after Citigroup Inc (C.N) reported quarterly earnings.

The index futures turned negative earlier in the morning after Goldman Sachs Group (GS.N) also announced its third-quarter results.

S&P 500 futures SPc1 fell 5.5 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 DJc1 fell 44 points, and Nasdaq futures NDc1 lost 9.75 points.