How many believers are there around the world?

If you think religion belongs to the past and we live in a new age of reason, you need to check out the facts: 84% of the world’s population identifies with a religious group. Members of this demographic are generally younger and produce more children than those who have no religious affiliation, so the world is getting more religious, not less – although there are significant geographical variations.

According to 2015 figures, Christians form the biggest religious group by some margin, with 2.3 billion adherents or 31.2% of the total world population of 7.3 billion. Next come Muslims (1.8 billion, or 24.1%), Hindus (1.1 billion, or 15.1%) and Buddhists (500 million, or 6.9%).

The next category is people who practise folk or traditional religions; there are 400m of them, or 6% of the global total. Adherents of lesser-practised religions, including Sikhism, Baha’i and Jainism, add up to 58m, or well below 1%. There are 14m Jews in the world, about 0.2% of the global population, concentrated in the US and Israel.

But the third biggest category is missing from the above list. In 2015, 1.2 billion people in the world, or 16%, said they have no religious affiliation at all. This does not mean all those people are committed atheists; some – perhaps most – have a strong sense of spirituality or belief in God, gods or guiding forces, but they don’t identify with or practise an organised religion.

Almost all religions have subdivisions. Christians can be Roman Catholic (the biggest group with almost 1.3 billion adherents), Protestants, Eastern Orthodox, Greek Orthodox, Anglican or many other sub-denominations. Muslims might be Sunni (the majority), Shia, Ibadi, Ahmadiyya or Sufi. Hinduism has four main groups: Vaishnavism, Shaivism, Shaktism and Smartism. There are two main traditions in Buddhism – Theravāda and Mahayana, each with subgroups. Jews can be Orthodox (or ultra-Orthodox), Conservative, Reform or belong to smaller groups.

Geography is important in religion. Asia-Pacific is the most populous region in the world, and also the most religious. It is home to 99% of Hindus, 99% of Buddhists, and 90% of those practising folk or traditional religions. The region also hosts 76% of the world’s religiously unaffiliated people, 700m of whom are Chinese.

Three-quarters of religious people live in a country where they form a majority of the population; the remaining quarter live as religious minorities. For example, 97% of Hindus live in three Hindu-majority countries: India, Mauritius and Nepal, while 87 %% of Christians live in 157 Christian-majority countries. Three-quarters of Muslims live in Muslim-majority countries. Among the religiously unaffiliated, seven out of 10 live in countries where they are in the majority, including China, the Czech Republic and North Korea.

In contrast, most Buddhists (72%) live as a minority in their home countries. There are seven countries where Buddhists form the majority of the population: Bhutan, Myanmar, Cambodia, Laos, Mongolia, Sri Lanka and Thailand.

Which religions are growing, and where?

The short answer is religion is on the wane in western Europe and North America, and it’s growing everywhere else.

The median age of the global population is 28. Two religions have a median age below that: Muslims (23) and Hindus (26). Other main religions have an older median age: Christians, 30; Buddhists, 34 and Jews, 36. The religiously unaffiliated come in at 34.

Islam is the fastest-growing religion in the world – more than twice as fast as the overall global population. Between 2015 and 2060, the world’s inhabitants are expected to increase by 32%, but the Muslim population is forecast to grow by 70%. And even though Christians will also outgrow the general population over that period, with an increase of 34% forecast mainly thanks to population growth in sub-Saharan Africa, Christianity is likely to lose its top spot in the world religion league table to Islam by the middle of this century.

Hindus are set to grow by 27%, and Jews by 15% mainly because of the high birth rate among the ultra-Orthodox. The religiously unaffiliated will see a 3% increase. But proportionately, these religious groupings will be smaller than now because their growth is lower than the increase in the overall global population. And Buddhists are forecast to see a 7% drop in their numbers.

It’s mainly down to births and deaths, rather than religious conversion. Muslim women have an average of 2.9 children, significantly above the average of all non-Muslims at 2.2. And while Christian women have an overall birth rate of 2.6, it’s lower in Europe where Christian deaths outnumbered births by nearly 6 million between 2010 and 2015. In recent years, Christians have had a disproportionately large share of the world’s deaths (37%).

And while the religiously unaffiliated currently make up 16% of the global population, only about 10% of the world’s newborns were born to religiously unaffiliated mothers between 2010 and 2015.

But 23% of American Muslims say they are converts to the faith, and in recent years there has been growing anecdotal evidence of Muslim refugees converting to Christianity in Europe.

China has seen a huge religious revival in recent years and some predict it will have the world’s largest Christian population by 2030. The number of Chinese Protestants has grown by an average of 10 % annually since 1979, to between 93 million and 115 million, according to one estimate. There are reckoned to be another 10-12 million Catholics.

In contrast, Christianity is in decline in Western Europe. In Ireland, traditionally a staunchly Catholic country, the proportion of people identifying with Catholicism fell from 84.2% to 78.3% between the two censuses of 2011 and 2016, and down to 54% among people aged between 16 and 29. Those with no religious affiliation increased to 9.8% – a jump of 71.8% in five years.

In Scotland, another country steeped in religious tradition, a majority of people, 59%, now identify as non-religious – with significantly more women (66%) than men (55%) turning away from organised faith. Seven in 10 people under the age of 44 said they were non-religious; the only age group in which the majority are religiously affiliated is the over-65s.

What about theocratic states?

The Islamic Republic of Iran is probably the one that springs to mind first. Until the 1979 revolution, the country was ruled by the Shah, or monarch. But the leader of the new state was the Ayatollah Ruhollah Khomeini, who implemented a political system based on Islamic beliefs and appointed the heads of the judiciary, military and media. He was succeeded in 1989 by Ayatollah Ali Khamenei. There is an elected president, currently Hassan Rouhani, who is considered a moderate, reformist figure. Iran is one of only two countries in the world that reserves seats in its legislature for religious clerics (the other is the UK).

Other Islamic theocracies are Mauritania, Saudi Arabia, Sudan and Yemen. Twenty-seven countries enshrine Islam as their state religion.

The only Christian theocracy is Vatican City, the tiny but powerful centre of Roman Catholicism, where the Pope is the supreme power and heads the executive, legislative and judicial branches of the Vatican government.

Thirteen countries (including nine in Europe) designate Christianity or a particular Christian denomination as their state religion. In England, the Anglican church – the Church of England – is recognised as the official “established” church of the country with important roles relating to state occasions. Twenty-one bishops sit in the House of Lords by right.

Israel defines itself as the “Jewish state”, with an 80% majority Jewish population. However the government is secular.

In 2015, more than 100 countries and territories have no official or preferred religion.

What religions are oldest and are there any new ones?

The oldest religion in the world is considered to be Hinduism, which dates back to about 7,000 BCE. Judaism is the next oldest, dating from about 2,000 BCE, followed by Zoroastrianism, officially founded in Persia in the 6th century BCE but its roots are thought to date back to 1,500 BCE. Shinto, Buddhism, Jainism, Confucianism and Taoism bunch together around 500-700 BCE. Then along came Christianity, followed about 600 years later by Islam.

Some might argue that the newest religion is no religion, although non-believers have been around as long as humans. But periodically new religious movements spring up, such as Kopimism, an internet religion, the Church of the Flying Spaghetti Monster or Pastafarianism (officially recognised by the New Zealand government but not the Dutch), and Terasem, a transreligion that believes death is optional and God is technological.

In 2016, the Temple of the Jedi Order, members of which follow the tenets of the faith central to the Star Wars films, failed in its effort to be recognised as a religious organisation under UK charity law. In the last two censuses, Jedi has been the most popular alternative religion with more than 390,000 people (0.7% of the population) describing themselves as Jedi Knights on the 2001 census. By 2011, numbers had dropped sharply, but there were still 176,632 people who told the government they were Jedi Knights.

Does religion have an impact on the world?

Of course – there are huge consequences to religious belief and practice. Firstly, countless wars and conflicts have had an overt or covert religious dimension throughout history right up to the present day. In the past few years, we’ve seen Islamic extremists waging war in the Middle East, a power struggle between Sunni and Shia across the region, the persecution of Rohingya Muslims in Myanmar, the Boko Haram insurgency in Nigeria, violent clashes between Christians and Muslims in Central African Republic, to name a few. Women are subjugated, LGBT people are persecuted, and “blasphemists” are tortured and murdered in the name of religion.

Then there’s the political impact. Donald Trump won the 2016 presidential election with the overwhelming support of white evangelical Christians. Legislators in Argentina recently voted against legalising abortion under pressure from Catholic bishops and the pope. Hungary’s far-right prime minister, Viktor Orbán, has cited the need to protect his country’s “Christian culture” to justify his anti-immigration policies.

But it’s not all bad news. There are millions of people of faith across the world engaging in social action projects to help the poor and marginalised. Look at the involvement of churches, mosques and synagogues in food banks and projects to support refugees, the sanctuary church movement in the US, the extraordinary sums raised by Islamic charities for relief work in some of the world’s most desperate places.

What happens next?

More prejudice and persecution. Followers of most major religions report increasing hostility and, in many cases, violence. Christians have been largely driven out of the Middle East, with some calling it a new genocide. Meanwhile antisemitism and Islamophobia are rising in Europe.

One of the biggest upheavals on the religious landscape in the next few years is likely to be the death (or, possibly, retirement) of Pope Francis, who is 81 and has a number of health issues. His efforts to reform the Vatican and the church have led to a significant backlash by conservative forces, who are organising against his papacy and preparing for the moment when the post becomes vacant.

Further reading

A Little History of Religion by Richard Holloway

Jerusalem: The Biography by Simon Sebag Montefiore

A History of God: The 4,000-Year Quest of Judaism, Christianity, and Islam by Karen Armstrong

The Caliphate by Hugh Kennedy

The God Delusion by Richard Dawkins

God Is Not Great: How Religion Poisons Everything by Christopher Hitchens

The Bible

The Qur’an