Answers to Quora Questions by Yair Davidiy (1 January 2017, 14 Tevet, 5778)
How many non-ultra-Orthodox Jews become ultra-Orthodox? Have most ultra-Orthodox adults been raised in ultra-Orthodox households?
As we said some leave but the net increase is still significant. On the other hand the National Religious lose a lot, maybe from 40% to 50%, or maybe less but still high. This loss is partly made up by secular Jews becoming NRs and by the larger families of they who remain within the fold. A related phenomenon is for the more learned among the NRs to draw closer to the Ultra-Orthodox.
The two main centers of Jewish Orthodoxy today are in Israel and the USA. In America the situation is different but here too the Ultra-Orthodox are growing.