Keep this baseline in mind: on average worldwide, each additional year of schooling yields a personal return of roughly 9% per year

No cost at all. Memorize this figure and use it as a benchmark for evaluating any “learning opportunity.”

A comprehensive review covering 1120 estimates from 139 countries between 1950 and 2014 found that the worldwide average private return on each additional year of schooling is 9% per year. This private return is the portion that directly affects an individual’s earnings — on average, an extra year of schooling raises income by 9%. The private return on higher education is on the rise, while the social return on education (the benefit to society as a whole) remains substantial. Women continue to reap higher average returns than men from schooling.

Psacharopoulos G, Patrinos HA (2018). Returns to investment in education: a decennial review of the global literature. Education Economics, 26(5), 445-458. https://doi.org/10.1080/09645292.2018.1484426；世界银行政策研究工作论文 8402. https://doi.org/10.1596/1813-9450-8402

This is a global average for "one more year of school." It is not the return to "signing up for a course," and it is not a China-specific figure. It is only a scale reference. Its use is to give every training plan a yardstick. If a course costs you 30000 yuan (3万) and six months, ask whether it can bring an income change on the scale of one year of formal education. Also note that the global average hides large differences by subject and by country