Spain calls this the Régimen Especial para Trabajadores Desplazados, officially Article 93 of the Ley del IRPF, but everyone just calls it the Beckham Law, after the footballer who became its most famous early beneficiary. If AEAT (Spain's tax agency) approves your application, your Spanish-source salary stops being taxed under the normal progressive IRPF bands and instead gets a flat 24% up to €600,000 a year, 47% above that. No personal allowance stacking, no regional variation, just one flat number applied to your gross salary.
The catch is eligibility. You need to not have been a Spanish tax resident in the five tax years immediately before you move (that lookback used to be ten years before the 2023 Startup Law shortened it), and you have to file your application within six months of registering with Spanish Social Security. Once approved, the regime runs for the year you become resident plus five more, six tax years total, then you revert to standard IRPF whether you like it or not.
The standard-regime side of this calculator uses Madrid's combined state-plus-regional IRPF scale, since Madrid runs one of the lowest regional add-ons in the country and is the most commonly cited "standard" benchmark for tech hires. If your real alternative is Catalonia or Valencia instead, where the regional scale runs meaningfully higher, the Beckham Law advantage you'd actually see would be even bigger than what's shown here.
Social Security is unaffected by which income-tax regime you're on: both columns apply the same 6.50% employee contribution, capped at €61,214.40 a year for 2026 (the base máxima de cotización), so every euro of difference you see between the two columns comes from the income-tax line alone.