U.S. stock index futures extended losses on Tuesday after a broad stock rally in the previous session that took the S&P 500 to its best day in two months and as investors fretted over whether Greece could make deep spending cuts.

S&P 500 futures were down 8.5 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 45 points, while Nasdaq 100 futures dipped 14.50 points.

(Reporting by Edward Krudy; Editing by Padraic Cassidy)