On the same $150,000 gross, a worker takes home roughly ¥7,750 more per year in Japan than in Singapore. That gap reflects the tax structure alone — before rent, healthcare, or savings behaviour come into play.
Housing is the first multiplier. Japan has moderate rent pressure, while Singapore has very high rent pressure. That keeps Japan's nominal advantage closer to a real-world advantage.
Healthcare and pensions go in the opposite direction. Japan runs a universal healthcare model — Universal Shakai Hoken with 30% patient co-pay; very low absolute costs. Singapore uses a mixed model — MediSave/MediShield is mandatory for citizens & PRs; expats use private cover. The country with lower take-home often shifts costs that the other country leaves to your private budget.
Net-of-everything, a relocation decision should weigh comprehensive welfare state in Japan against balanced public welfare in Singapore, plus differences in pension capture, social safety nets, and city-level cost of living.