Calculating Box 3 tax on rental income (2026)

A common misconception: in box 3 you pay tax on the rent you receive. That is not how it works. Box 3 taxes a forfaitary return — a return assumed by law on your wealth — regardless of what you actually collect in rent.

How it works

Since the bridging law (Overbruggingswet), the tax office splits your wealth into categories, each with its own assumed return. A rental property falls under "other assets", with a relatively high forfaitary percentage. Debts (such as a mortgage) count with a lower forfait. Simplified:

1. Asset return = property value × forfait for other assets.
2. Debt deduction = debt × forfait for debts.
3. Return = asset return − debt deduction.
4. On the part of your net wealth above the tax-free allowance you pay the box 3 rate on this return.

Because the debt forfait is lower than the asset forfait, a mortgage only modestly reduces the taxable return — financed letting is taxed relatively heavily in box 3.

Run the numbers

Why this matters

The forfaitary system can work out poorly if your actual return is lower than the assumed one. A move toward taxing actual returns is underway; until then you calculate with the forfaitary method. Keep your real income and costs — you need them to provide counter-evidence or consider an objection.

Note: the forfaitary percentages, tax-free allowance and rate for 2026 are indicative and not yet final. Verify the current figures with the Belastingdienst.