Stock index futures fell to session lows on Tuesday weighed down by financial shares and by caution ahead of the Federal Reserve's two-day policy meeting, pointing to a lower open on Wall Street.

S&P 500 index futures were down 5.9 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 48 points, while Nasdaq 100 futures dipped 9.75 points.

(Reporting by Rodrigo Campos; Editing by Padraic Cassidy)