I lifted the following from the Faith Central blog. Sorry for the funky formatting:
1. Islam: Growth rate 1.84 per cent* with 1.3 billion followers worldwide
2. Baha'i faith: Growth rate 1.70 per cent with 7.7 million followers worldwide
3. Sikhism: Growth rate 1.62 per cent with 25.8 million followers worldwide
4. Jainism: Growth rate 1.57 per cent with 5.9 million followers worldwide
5. Hinduism: Growth rate 1.52 per cent with 870 million followers worldwide
6. Christianity: Growth rate 1.38 per cent with 2.2 billion followers worldwide
*rate of change of adherants to this religion between 2000-2005 as a percentage per year
Atheism is growing at a rate of 1.39 per cent and Afghanistan has the fastest growing population of Atheists.
Where are faiths growing fastest?
Faith Where is it growing fastest?
Baha'i faith Qatar
Buddhism New Zealand
Chinese Universalism Finland
Roman Catholicism Sierra Leone
Confucianism Northern Mariana Islands
Hinduism United Arab Emirates
Islam Soloman Island (followed by Norway)
Neo Religionism United Arab Emirates
Sikhism United Arab Emirates
Figures taken from the World Christian Database