NEW YORK, Sept 24 (Reuters) - 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 SPc1> 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 DJc1> gained 34 point and Nasdaq 100 futures NDc1> added 9 points. (Reporting by Chuck Mikolajczak; Editing by Padraic Cassidy)