In the US, more than 45% of those age 18 or over are single, with the number in China about 15% (200 million people). The increase in singles is expected to have enormous consequences on housing, healthcare, population levels and consumer habits.

For Ashley Gray, a 26-year-old web developer living on the Upper West Side of Manhattan, her best time is in the evening, after a long and tiring day at work — and when she is alone.

"I will cook my own dinner – I can eat whatever I want, and I will go to the gym, then get beers and watch my favorite shows on Netflix," said Gray, who has been single for about five years after breaking up with her college boyfriend. "Or I can choose to hang out with my friends."

She said she likes to be free to go with the flow and be responsible only for herself, and not having to compromise.

"I just feel like I'm happier and more myself [when I'm alone]," Gray said, adding she's also busy trying to advance her career, so she doesn't want to spend extra time on taking care of a partner or children if she gets into a relationship or gets married.

"So, I think I won't get married until I'm 33," Gray said.

Like Gray, more women and men in the US are single — more than 45 percent of all Americans age 18 or older, the US Census Bureau reported in 2017 — and the number of single households around the world also is increasing.

Singles make up about 14.6 percent — about 200 million — of China's population, the largest singles population in the world, People's Daily reported.

Sweden has the highest rate of people staying single, 51 percent of all households, according to 2017 data from the European Union's Eurostat.

Sweden is followed by Denmark, Finland and Germany, which all have more than 40 percent one-person households.

The never-married population age 16 years and over in England and Wales increased by 3.9 million from 2002 to 2017, while the number of married people increased only by 1.2 million during the same period, UK Census reported.

Factors contributing to the rise of one-person households include new views on marriage, high levels of divorce, increased education that leads to more employment and better-paying career opportunities, and increased longevity and improved health at older ages.

The growth of one-person households could have numerous consequences for society, ranging from housing and health care to the fertility rate and consumption patterns, say experts.