On the same 65 000 € gross, a worker takes home roughly 5 076 € more per year in Belgium than in Netherlands. That gap reflects the tax structure alone — before rent, healthcare, or savings behaviour come into play.
Housing is the first multiplier. Belgium has moderate rent pressure, while Netherlands has very high rent pressure. That keeps Belgium's nominal advantage closer to a real-world advantage.
Healthcare and pensions go in the opposite direction. Belgium runs a universal healthcare model — Mutuelle/ziekenfonds covers most costs after a small co-pay. Netherlands uses a public model — Mandatory private health insurance (~€140/month) with regulated coverage. 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 Belgium against comprehensive welfare state in Netherlands, plus differences in pension capture, social safety nets, and city-level cost of living.