Stock index futures trimmed gains and were well off their session highs on Tuesday after Freddie Mac, the No. 2 U.S. mortgage finance company, posted a wider third-quarter loss.

S&P 500 futures were up 5.5 points, above fair value, a mathematical formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. S&P futures were earlier up as much as 12 points.

Dow Jones industrial average futures rose 61 points, and Nasdaq 100 futures gained 19 points.

Freddie Mac shares fell 4.8 percent to $35.75 in trading before the bell.

(Reporting by Jennifer Coogan; Editing by Kenneth Barry)