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. Poland has moderate rent pressure, while Czech Republic 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. Poland runs a public healthcare model — NFZ public system with growing private supplements. Czech Republic uses a public model — Statutory health insurance covers essentially all care. 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 Poland against strong public welfare in Czech Republic, plus differences in pension capture, social safety nets, and city-level cost of living.