The Netherlands: two credits that quietly raise your marginal rate
Dutch box 1 tax looks simple, three brackets at 35.75%, 37.56% and 49.50%. The first rate is mostly not income tax at all: 8.10% is wage tax and 27.65% is national insurance for the state pension, survivors' benefit and long-term care. Reach state pension age and the AOW part falls away, dropping the first bracket to 17.85%.
What actually shapes a Dutch payslip is the pair of tax credits. The general credit (algemene heffingskorting) starts at €3,115 and tapers away at 6.398% from €29,736. The labour credit (arbeidskorting) climbs to about €5,685 at €45,592 and then falls at 6.51%. Between roughly €30,000 and €78,000 you are losing both at once, so each extra euro is taxed far above the headline bracket rate even though the bracket has not changed.
Two more things matter. Dutch salaries are usually quoted without the 8% holiday allowance, paid as a lump sum in May, so the calculator asks whether your figure includes it. And the 30% ruling lets qualifying incoming employees receive up to 30% of salary tax-free, provided the taxable remainder stays above €48,013 (or €36,497 if you are under 30 with a master's), which is why the exemption shrinks at lower salaries.
Box 1 tax: 35.75% on €38,883 = €13,900.67, plus 37.56% on €11,117 = €4,175.55.
Credits: general €1,818.51 plus labour €5,398.04 = €7,216.55, leaving €10,859.67 of tax.
Take-home: €39,140.33 a year, €3,261.69 a month, an effective rate of 21.7%, while the marginal rate on the next euro is above 45% because both credits are still tapering.