One in nine Korean men aged 45 to 54 have either decided to stay single or are having problems getting married.
Analysis of 2015 census data shows that some 10.9 percent of men in the age group have never been married, compared to just five percent of women in the same age group. This is the first time that the rate has risen above 10 percent.
In 1985, there were almost no men or women in the age bracket who had never been married, at 0.4 percent and 0.3 percent. But the proportion started rising steadily after 2000.
Lee Sang-lim at the Korea Institute for Health and Social Affairs said, "The surging number of middle-aged people who stay single all their lives appears to be due to economic slump that has persisted since the Asian financial crisis some 20 years ago, which made it difficult for many to find jobs."
Another factor is changing social attitudes where marriage no longer looks like the be-all and end-all, Lee added. The growing number of women in the workforce also meant that more of them decided they can manage economically without a husband.
Rural Gangwon Province has the highest proportion of single middle-aged men at 13.2 percent, followed by Busan (13.1 percent), South Jeolla Province (12.4 percent), Seoul (12.3 percent) an Jeju Island (12.1 percent).
In the countryside the phenomenon is mostly driven by circumstances rather than choice. Gangwon, South Jeolla provinces and other rural regions tend to have high proportions of bachelors because the marriage rate is typically low among men with lower levels of education and women avoid moving into farming communities.
But in the cities, individual choice seems more decisive. Seoul has the highest proportion of women who have been single their whole lives at 7.4 percent, followed by Jeju Island (6.9 percent), Busan (5.8 percent) and Sejong (5.7 percent). That suggests highly-educated, urban women with solid incomes tend to avoid tying the knot.
The southeastern port city of Ulsan, which boasts the highest average income in the nation but is mostly industrial, has the lowest proportion of both men and women who have been single their whole lives.
Experts forecast that Korea could overtake Japan 15 years from now in terms of confirmed singles. In Japan the proportion for men was 23.4 percent in 2015 and for women 14.1 percent.
But Korea is similar or ahead of Japan when it comes to singles in their 30s, many of whom end up staying single into middle age, at 44.2 percent for men compared to Japan's 40.6 percent, and 28.1 percent for women compared to 28.9 percent in Japan.
Cho Young-tae at Seoul National University said, "In a culture that frowns on childbirth out of wedlock, a rising number of single people has a direct impact on the birthrate." He said one solution would be to remove hurdles at least for those singles who want to get married but cannot afford to, like the high cost of weddings and dowries.