When you emigrate from the Netherlands, the Belastingdienst splits that calendar year into a period as a domestic taxpayer and a period as a foreign taxpayer. You file that year with the M-form (M-aangifte), not the ordinary income tax return. Because your employer withheld wage tax as though you worked in the Netherlands the whole year, the departure year commonly produces a refund. Taxmo files the M-form directly to the Belastingdienst from €129 incl. VAT.
Up to your departure date you are a domestic taxpayer and your worldwide income counts. After that date you are a foreign taxpayer and only your Dutch-source income counts, such as a final salary, a Dutch benefit, or rent from a Dutch property. The M-form handles that split automatically, box by box.
Did you build up pension or annuity entitlements with tax relief, hold a substantial shareholding in a bv, or carry a capital insurance tied to your own home? The Belastingdienst can issue a conservatory assessment at departure over the tax advantage you held until then. For the capital insurance tied to an own home you do not have to pay it as long as the property stays your own home, and it can lapse after 10 years.
The screening questions tell you straight away whether your departure year can be filed online. From there you go through your last Dutch income, a fiscal partner if you have one, your own home, the pension claims an emigrant must report, and box 2 or box 3 where they apply. You only pay once the return is ready to file.