Answer
According to Pew Research Center, Christianity remains the world’s largest religious group at 31.2 percent of the earth’s 7.3 billion people. Next is Islam (24.1 percent), unaffiliated (16 percent), Hinduism (15.1 percent), Buddhism (6.9 percent), folk religions (5.7 percent), other (0.8 percent), and Judaism (0.2 percent).
Pew Research Center defines Christianity as a single religious group, and no set of beliefs or practices was used to define who is a Christian. The study simply used self-identification—if a person claimed to be a Christian, he or she was counted in the “Christian” group.
Within the label of “Christianity” are several subdivisions. Approximately 50 percent of the people labeled Christians identify as Catholic, while 37 percent labeled themselves as Protestant (including Anglicans). Orthodox communities made up 12 percent of the Christians in the study. Other groups make up the final 1 percent: Mormons, Christian Scientists, and Jehovah’s Witnesses.
What percentage of people in the world are truly Christian, i.e., what percentage of people in the world are trusting in Jesus as personal Savior, by grace alone through faith alone? There is no way to know the answer to that question. Considering Jesus said, “small is the gate and narrow the road that leads to life, and only a few find it” in Matthew 7:14, it is highly unlikely that the number of true Christ-followers is anywhere near 50% of the world’s population.
Sources:
http://www.pewresearch.org/fact-tank/2017/04/05/christians-remain-worlds-largest-religious-group-but-they-are-declining-in-europe/
http://assets.pewresearch.org/wp-content/uploads/sites/11/2017/04/04104610/Appendix-E-DefiningReligiousGroups.pdf
