Our summary
A new position from the Tax Authority's knowledge group clarifies that when refinancing a mortgage, the original 30-year repayment term must be maintained. If a new 30-year term is agreed upon for the remaining debt, the mortgage may lose its Box 1 status and move to Box 3, resulting in the loss of mortgage interest deduction.
Summarised in plain language by NL Tax Calculator. Accountancy Vanmorgen has the full story, with every detail.