U.S. stock index futures added to gains on Thursday after data showed the number of U.S. workers filing new claims for jobless benefits unexpectedly fell by 21,000 last week.

* S&P 500 futures rose 4.1 points and were above 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 gained 34 point and Nasdaq 100 futures added 9 points.

(Reporting by Chuck Mikolajczak; Editing by Padraic Cassidy)