Netherlands
Most commonly Box 1 income at ~37/49.5%, with a contested minority Box 3 argument. Structural traders may register as ZZP to deduct costs. Classification is unsettled.
Usually Box 1 — 'resultaat uit overige werkzaamheden' (income from other activities) or business profit. A minority view argues Box 3 (wealth). Genuinely debated.
Box 1 progressive — ~36.97% up to ~€75,500 and 49.5% above (2025/26).
National-insurance premiums are folded into the first Box 1 bracket; income-dependent Zvw health contribution. No mandatory self-employed pension.
If business-like, register as ZZP/eenmanszaak (KvK) for cost deductions; otherwise declare as 'overige werkzaamheden'.
USDC is Box 1 income at EUR value on receipt; under the contested Box 3 view it would instead be taxed as an asset.