The U.S. has been steadily losing its religion for decades. For the most part, Protestants have been leaving the church while the affiliation rates among Catholicism and other religions in the country have remained stable. But since 1990, Americans have been abandoning both belief and religious affiliation at such a fast pace that, by 2035, it's likely that 35 percent of the population will have no religious affiliation — outnumbering protestants.

In an article posted on his blog, Allen Downey, a professor of computer science at Olin College, used historical data from the General Social Survey (GSS) to generate predictions about the future of religious belief in the U.S., each with a 90 percent confidence interval

Downey wrote:

“According to the Theory of Secularization, as societies become more modern, they become less religious. Aspects of secularization include decreasing participation in organized religion, loss of religious belief, and declining respect for religious authority.

Until recently the United States has been a nearly unique counterexample, so I would be a fool to join the line of researchers who have predicted the demise of religion in America. Nevertheless, I predict that secularization in the U.S. will accelerate in the next 20 years.”

The graph above was generated using data from the GSS question that reads: “What is your religious preference: is it Protestant, Catholic, Jewish, some other religion, or no religion?”

Downey summarized his findings on religious affiliation in the U.S.:

  • The fraction of people with no religious affiliation has increased from less than 10% in the 1990s to more than 20% now. This increase will accelerate, overtaking Catholicism in the next few years, and probably replacing Protestantism as the largest religious affiliation within 20 years.
  • Protestantism has been in decline since the 1980s.  Its population share dropped below 50% in 2012, and will fall below 40% within 20 years.
  • Catholicism peaked in the 1980s and will decline slowly over the next 20 years, from 24% to 20%.
  • The share of other religions increased from 4% in the 1970s to 6% now, but will be essentially unchanged in the next 20 years.

In addition to religious affiliation, Americans also seem to be losing their religious belief — at least strong belief, as Downey's model shows.

Downey also used GSS data to make predictions about people's interpretations of the bible. well as their confidence in religious institutions.

Startling as the numbers may be, there's reason to think these projections are actually conservative, considering:

  • Social desirability bias — On surveys like these, people tend to tilt their answers toward whatever is socially acceptable to say. Considering being atheist or nonreligious is stigmatized in many parts of the country, some people may be claiming allegiance to a religion when in fact they're nonreligious.
  • The 1990 inflection point — Around 1990, rates of religious affiliation seemed to be significantly disrupted, with a major drop-off among the Protestants. Any projections that factor in the data before 1990 might be too conservative seeing as the trend toward nonreligious affiliation has become more drastic in the past two decades. 

Although religion seems to be dying out in the U.S., other forms of spirituality might be just as present as ever.

A 2014 Pew study found that, between 2007 and 2014, the percentage of Americans who felt a "deep sense of spiritual peace and well-being" had increased from 52 to 59 percent, while the percentage of those who felt a "deep sense of wonder about the universe" increased from 39 to 46 percent.