SEIKO, a 35-year-old journalist in Tokyo, is what the Japanese refer to as “New Year Noodles”. The year ends on December 31st, and, by analogy, the period when a Japanese woman is deemed a desirable marriage prospect ends after 31. It could have been worse: the slang term used to be “Christmas cake” because a woman’s best-before date was considered to be 25.

Soon a new expression may be needed: men and women in Japan are marrying later, or sometimes not at all. Since 1970 the average age of first marriage has risen by 4.2 and 5.2 years for men and women respectively, to 31.1 and 29.4. The proportion of Japanese who had never married by the age of 50 rose from 5% in 1970 to 16% in 2010 (see chart).

Something similar is happening in other rich countries, but Japan leads the way in Asia. (The proportion of South Koreans who have never married by 50 is 4%, for example.) And whereas, in the West, the decline of marriage has been accompanied by a big rise in the number of unmarried couples living together, only around 1.6% of Japanese couples cohabit in this way. So in Japan fewer marriages means fewer babies—a calamity for a country with a shrinking and ageing population. Only 2% of Japanese children are born outside marriage, compared with over 40% in Britain and America. Some of the reasons for the flight from marriage in Japan are the same as in other rich countries. Women are better educated, pursue careers, can support themselves financially and don’t see the traditional family as the only way to lead a fulfilling life. Some of the details are different in Japan, however. Couples are expected to have children shortly after getting married, so women who want to delay childbearing have a strong incentive to delay marriage. Even so, a large majority of Japanese still want to get married eventually: 86% of men and 89% of women, according to a survey published in 2010 by the National Institute of Population and Social Security Research, a government agency.

Economics is a big part of the problem. Women seek men with financial security. Men want to be able to provide it. This is hard, however, when more and more young ones are stuck in temporary or part-time jobs. “I don’t want my wife and children to miss out on experiences because we can’t afford them,” says Junki Igata, a 24-year-old trainee at an international hotel chain, who says he will put off marriage until his mid- or late thirties. Men in part-time jobs are less likely to be married than full-timers.

The opposite holds for women: there are more unmarried women among full-time professionals than part-time ones. The problem for them is the persistence of a traditional view of marital responsibilities, which makes it especially hard for a Japanese woman to juggle a full-time career with children. Her husband will often want her to give up work. (Seiko’s boyfriend asked her to do so after only three months together; she refused.) Also, domestic chores are unevenly shared in Japanese marriages: men do only an hour and seven minutes of housework and child care a day, compared with around three hours in America and two-and-a-half hours in France.

People are finding it harder to meet, too. The days of omiai, or arranged marriage, are more or less gone. University students spend their free time joining clubs to bolster their CVs as good jobs become scarcer. Workers toil for long hours. Some reckon men in particular have become shyer (or lazier) about approaching prospective mates.

High expectations pose another barrier. Takako Okiie, a “concierge” at Partner Agent, a sleek matchmaking agency manned by perfectly made-up women, says clients are often all “me, me, me”. They want a dream partner (Ms Okiie says it takes 18 months to knock this out of them) or, at the very least, what Japan refers to as the “three averages”: average income, average looks, average education.

The difficulty young Japanese have in pairing up is one reason why the fertility rate has plunged. The number of children a Japanese woman can expect to have in her lifetime is now 1.42, down from 2.13 in 1970. Little wonder the population is shrinking.

Some fret about a rise in the number of isolated people and “parasite singles”: people who live with and depend on their parents well into adulthood. The state can provide economic support, but the sort of civic groups and community associations that help people feel integrated into society have weakened in Japan as elsewhere. The once-tight connection between workers and their company has loosened too with the decline of jobs for life. “I worry about what will happen when these people’s parents die,” says Masahiro Yamada, a sociologist at Chuo University who coined the term “parasite single”.

Not many singletons have boyfriends or girlfriends, even if they are neither otaku (men who are obsessed with anime or computer games) nor hikikomori (those who lock themselves away in their rooms). Mr Yamada reckons that if people aren’t marrying and aren’t dating, they must be doing something to satisfy their need for intimacy. He is researching whether they are opting for sexual and romantic alternatives such as prostitutes, romantic video games, celebrity obsessions, pornography or pets.

Shinzo Abe, the prime minister, is concerned. His government wants women to have more babies. It would also like marriage to remain the basis of family life. It has paid subsidies to towns that organise dating events, tried to create more nursery places and this week announced a bid to scrap a spousal tax break that discourages married women from earning more than 1.03m yen ($10,000) a year.

Such tinkering may help at the margins. So too would shorter working hours and—more important—an acceptance by Japanese men that they can’t get married on the terms their fathers did. Governments are mostly powerless to direct such cultural change, however. Japanese men and women will either have to figure out ways to live together—or remain alone.