On the same 65.000 € gross, a worker takes home roughly 4868 € more per year in Spain than in Italy. That gap reflects the tax structure alone — before rent, healthcare, or savings behaviour come into play.
Housing is the first multiplier. Italy has moderate rent pressure, while Spain 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. Italy runs a universal healthcare model — Universal SSN system, regionally administered, with private alternatives. Spain uses a universal model — Universal public healthcare via the SNS; private cover is widespread. 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 Italy against strong public welfare in Spain, plus differences in pension capture, social safety nets, and city-level cost of living.