The projections suggest that by 2070 the number of Muslims in the world will catch up with Christians, if current trends continue. They also suggest that by 2050 Muslims could account for 10% of Europe's population and that in the United States "Christians will decline from more than three-quarters of the population in 2010 to two-thirds in 2050, and Judaism will no longer be the largest non-Christian religion. Muslims will be more numerous in the U.S. than people who identify as Jewish on the basis of religion."
Overall, the global numbers could shift a bit depending upon what happens in China:
For example, China’s 1.3 billion people (as of 2010) loom very large in global trends. At present, about 5% of China’s population is estimated to be Christian, and more than 50% is religiously unaffiliated. Because reliable figures on religious switching in China are not available, the projections do not contain any forecast for conversions in the world’s most populous country. But if Christianity expands in China in the decades to come – as some experts predict – then by 2050, the global numbers of Christians may be higher than projected, and the decline in the percentage of the world’s population that is religiously unaffiliated may be even sharper.The key element here is especially the trend of the birth among Muslims, in particular, in various regions of the world--a topic that I have been following for a long time and which I referenced yesterday with respect to Iran.