On the same 150 000 zł gross, a worker takes home roughly 591 Kč more per year in Czech Republic than in Poland. That gap reflects the tax structure alone — before rent, healthcare, or savings behaviour come into play.
Housing is the first multiplier. Czech Republic has moderate rent pressure, while Poland has moderate rent pressure. The two markets behave similarly, so most of the gross-to-net advantage flows straight into disposable income.
Healthcare and pensions go in the opposite direction. Czech Republic runs a public healthcare model — Statutory health insurance covers essentially all care. Poland uses a public model — NFZ public system with growing private supplements. 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 strong public welfare in Czech Republic against strong public welfare in Poland, plus differences in pension capture, social safety nets, and city-level cost of living.