Family mortgage and box 3: what changes for lender and borrower

A family mortgage touches box 3 on both sides. The lender holds a claim (vordering) that counts as an asset. The borrower holds a debt that can reduce taxable wealth. Understanding both sides prevents surprises in the tax return.

For the lender: a box 3 asset

The outstanding loan is an asset in box 3, just like savings. The Belastingdienst taxes deemed returns on it under the forfaitary system, not the actual interest received. Whether the money sits in a savings account or in a family mortgage, box 3 treats it broadly the same.

The interest itself is not taxed separately in box 1 for most private lenders. It simply stays inside the box 3 deemed-return logic.

For the borrower: debt deduction

The borrower may deduct the family mortgage debt from box 3 assets, unless the loan qualifies for box 1 treatment as a home loan with deductible interest. Which box applies depends on the property and the loan structure, not on the family relationship.

Used for the own home with annuity repayment within 360 months? Then the loan and its deduction usually live in box 1. Used for anything else? The debt deduction lives in box 3.

FLUX5 keeps every figure the return asks for in one place: outstanding balance, interest paid, and the schedule. Both sides export their own numbers at tax time.