Plain Language Summary Fertility treatments have helped millions of people to have a child. Although financial factors are known to play an important role in the decision to use fertility treatments, no previous studies have investigated how socioeconomic factors affect medical help-seeking for fertility in Japan. Therefore, we assessed the association between household income and medical help-seeking among couples with fertility problems in Japan, using nationally representative data from the National Fertility Survey 2015. Of the 6598 respondents (married women under 50 years old), one-third (2253) reported worrying about fertility problems, and half of those women (1154) sought medical help for fertility-related issues. The proportion of...