How this mortgage calculator works

This calculator is designed to compare financial scenarios, not to deliver precise financial forecasts.

It helps explore questions such as:

• How do annuity and linear mortgages evolve over time?
• What happens if the monthly difference is invested instead of spent?
• How might mortgage interest tax relief and wealth tax affect the outcome?

All results are model-based approximations.

What is included

Mortgage calculations

• Annuity and linear mortgage models
• Monthly interest and principal calculations
• Remaining balance and total repayments per year
• Support for mortgages that already started in the past

Mortgage interest tax relief (HRA)

• Estimated based on paid mortgage interest
• Assumes eligibility and sufficient taxable income
• Calculated monthly at the interest level and aggregated yearly

Investment simulation

• Monthly investment of:
  • the difference between mortgage payments and a reference “interest-only” amount;
  • an optional additional monthly investment.
• Fixed average annual return, compounded monthly
• Separate tracking of:
  • main investment pile;
  • additional investments;
  • other existing assets.

Wealth tax (Box 3 – simplified)

• Applies the debt threshold once to total debts
• Uses a simplified model of:
  • tax-free allowance;
  • forfaitary returns;
  • annual tax correction.
• Includes an indicative estimate of “wealth tax saved” due to outstanding debts

What is not included

This calculator does not account for:

• Eigenwoningforfait
• Wet Hillen
• Income-dependent limits on mortgage interest tax relief
• Future tax law or policy changes
• Mortgage refinancing or consolidation logic
• Transaction costs such as:
  • advisory fees;
  • notary fees;
  • transfer tax;
  • early repayment penalties.
• Inflation or changes in purchasing power
• Investment volatility, drawdowns, or risk

Linear mortgage results may show minor rounding differences over long periods.

Important limitations

• Investment returns are assumed and not guaranteed
• Tax calculations are simplified representations, not official tax assessments
• This calculator does not replace professional financial, tax, or legal advice

Legal disclaimer

This calculator and all related content are provided “as is”, without any express or implied warranties.

To the maximum extent permitted by law:

• the author disclaims all liability for any loss or damage arising from use of this calculator;
• no responsibility is accepted for errors, inaccuracies, or outdated assumptions;
• users remain fully responsible for their own financial decisions.

By using this calculator, you acknowledge and accept these limitations.