Every other Dutch tax explanation assumes these three boxes are already understood, which leaves first-time filers reverse-engineering the vocabulary from a form. Box 3 in particular works unlike wealth or capital-gains taxation in most other countries, and misreading it is what produces the largest surprises.
Three boxes split up your income on a Dutch tax return, each taxed under its own rules. Box 1 covers income from work and your home — salary, benefits, self-employment profit, and the notional rental value (eigenwoningforfait) of an owner-occupied house minus mortgage interest deduction. For 2026 it's taxed progressively: 35.75% up to €38,883, 37.56% up to €78,426, and 49.50% above that. Box 2 catches income from a "substantial interest" — broadly, owning 5% or more of a company's shares — so dividends and sale gains from that stake. It's taxed at 24.5% up to €68,843 and 31% above, and fiscal partners can split that income between them to use both thresholds. Box 3 is the one that surprises people: it taxes savings and investments — bank balances, stocks, a second home, crypto — not on what they actually earned you, but on a deemed return calculated from your asset mix, at a flat 36% rate, after a tax-free allowance of €59,357 (€118,714 for fiscal partners together). Most employees only ever deal with Box 1 and, if their savings exceed the allowance, Box 3.