BackgroundA large proportion of adults in Japan remain unmarried even though they intend to marry during their lifetime. To provide data for policy makers and those searching for partners in the Japanese marriage market, we estimated the number and characteristics of unmarried women and men with marriage intention and assessed their partner preferences. Based on the findings, we hypothesized regarding potential mismatches between the individuals available in the marriage market and the type of partners they are looking for.MethodsWe used data from the National Fertility Survey (2015), a nationally representative survey in Japan, and included 20,344 participants aged 18–49 years, of which 6,568 were unmarried with marriage intention. We estimated the total number of unmarried women and men who intend to marry, extrapolated their characteristics to the Japanese population, and assessed their partner preferences, as well as their ideal age of marriage and the ideal age of their partner.ResultsIn 2015, there were 8.48 million unmarried women and 9.83 million unmarried men aged 18–49 years with marriage intention in Japan. Surpluses of around 600,000 men were observed in non-densely inhabited areas (men-to-women ratio: 1.31) and in the Kanto region (1.23). Most of the women and men in the marriage market had annual incomes lower than 3,000,000 JPY (28,000 USD) and only 263,000 women (3%) and 883,000 men (9%) had an income of 5,000,000 JPY (47,000 USD) or more; 167,000 men (2%) had an income of 7,000,000 JPY (66,000 USD) or more, with roughly three-quarters of them having a university degree. When asked about eight items that one may consider in a potential partner, the proportion of women listing an item as “important” tended to be larger than those of men across all items (education, occupation, finances, personality, mutual hobbies, cooperation/understanding regarding one’s work, and attitude towards/skills in housework and childrearing) except appearance. The largest differences were observed for finances (proportion of women vs. men listing the item as “important” or “would consider:” 94.0% vs. 40.5%, p<0.001), occupation (84.9% vs. 43.9%, p<0.001), and education (53.9% vs. 28.7%, p<0.001). While women, on average, preferred men who were around 1–3 years older than themselves, men preferred women around their own age until the age of 26 years, at which point men preferred women who were younger than themselves, with the preferred age difference increasing substantially with age. As such, the number of men preferring a younger partner was larger than the number of women who preferred an older partner.ConclusionsBy providing data on the number, characteristics and partner preferences of individuals in the marriage market, our study could inform decisions for those searching for marriage partners in Japan. Moreover, we hypothesize that mismatches in geographical location, the supply-demand disparity for partners with higher income, and age preferences could partly explain the large number of Japanese women and men who remain unmarried despite intending to get married. Further studies are needed to assess if, and to what extent, the identified mismatches may affect marriage rates.