People worldwide are becoming less religious in general, but religious people have more children.

The claim has two parts. Judge both as of 2018. (1) Secularisation: a majority of countries with survey data, such as World Values Survey or Pew, show declining religiosity over recent decades. The claim itself implies the global religious share may rise because of fertility, so this part can hold even if the global share of religious people grows. (2) Fertility: religious or affiliated people have higher fertility than nonreligious or unaffiliated people, globally or in most countries, as in Pew's 2015 Future of World Religions. True: both parts hold. Mostly true: both hold, with notable exceptions to the secularisation trend, such as parts of the former Soviet bloc or some developing countries. Mixed: only one part holds. Mostly false: the fertility gap holds, but religiosity is stable or rising in most countries. False: neither part holds.

Set before the research began.

1. E1 Giving Up on God Foreign Affairs · 11 August 2020

   “but we did find that in 33 of the 49 countries we studied, people became more religious during those years.”

2. E2 Giving Up on God Foreign Affairs · 11 August 2020

   “From about 2007 to 2019, the overwhelming majority of the countries we studied—43 out of 49—became less religious.”

3. E3 Religiously Unaffiliated Pew Research Center · 2 April 2015

   “Globally, the Total Fertility Rate (TFR) for the unaffiliated is 1.7 children per woman in the 2010-2015 period, while the rate for the world’s entire population is 2.5.”

4. E4 The Future of World Religions: Population Growth Projections, 2010-2050 Pew Research Center · 2 April 2015

   “All the other groups have fertility levels too low to sustain their populations: folk religions (1.8 children per woman), other religions (1.7), the unaffiliated (1.7) and Buddhists (1.6).”

On secularisation, E2 reports that 43 of the 49 countries studied became less religious from about 2007 to 2019, so most countries were secularising in the years up to 2018. E1, from the same study, says 33 of those 49 countries became more religious during a period the quoted text does not specify, so the trend is not uniform. On fertility, Pew's 2015 figures (E3, E4) put the unaffiliated at 1.7 children per woman against 2.5 for the world as a whole, which means religiously affiliated people have higher fertility overall. Both parts hold, but the earlier rise in religiosity is a notable exception, so the verdict is mostly true rather than true.