Complex sentence: Only 0.28% (3,220,000 people) of the expected Muslim population growth (1,161,780,000) in the period of 2010-2050 would be due to conversions; 99.72% would be due to a high birth rate among Muslims.
Split into simpler sentences: Only 0.28% (3,220,000 people) of expected Muslim population growth (1,161,780,000) in the period of 2010-2050 would be due to conversions. Rest 99.72% would be due to high birth rate among Muslims.