Not as easy to answer as you would think as, apart from Israel, there are no truly reliable statistics.
A lot depends on which USA survey result is believed. The 2000/2001 National Jewish Survey found 5.2 million, but a subsequent survey (involving Dr. Ira Sheskin) found and extra 1.4 million. This has been attacked by other Jewish demographers for 'double counting'.
I think the best estimate is about 13 million and if the former US survey is believed, Israel is already the largest Jewish community in the world.
What is important assessing future trends is to consider the births talking place. In the diaspora (of now < 8 million) there can only be some 70-80,000 births. In Israel the latest Jewish births figure is 106,000