About the project, method and contact
Who maintains Mortgage Planner, how the scenarios are calculated and how to report a problem.
An independent tool
Mortgage Planner is a free calculator from the HappyMaremmano project. It explores repayment of a known remaining principal at a fixed rate, with monthly principal-and-interest instalments. Results are simulations based on entered assumptions, not loan offers.
How the model works
The monthly rate equals annual nominal interest divided by twelve. The initial overpayment reduces principal before month one. A recalculates payments over the same term; B retains the original payment; C adds a monthly amount to B. Each schedule ends with actual repayment of the balance, including a smaller final instalment when needed.
Amounts are rounded to two decimals only for display or export. Entered fees are charged once to scenarios with extra payments and are not financed. The tool does not reconstruct interest-only loans, balloon payments, variable rates or changes in compounding convention.
Verification and transparency
The model is checked with independent numerical examples and tests for zero interest, full overpayments, partial final instalments, fees and invalid inputs. The guide makes the example reproducible. These checks validate the stated model; your lender’s contract may use different rules.
Issue reports
Email happymaremmano@gmail.com with your browser, device, steps and expected result. Use hypothetical amounts; do not send bank statements, documents, access codes or confidential financial information.
Support and advertising
The tool works without payment. A voluntary Buy Me a Coffee support link is provided. Any advertising requires separate setup and approval. Support arrangements do not change formulas or results. The site does not provide personalized mortgage offers or lender rankings.
Data
Numbers are processed locally. The calculator does not save them or add them to the shared link. CSV and print functions can retain a copy on your device. Statistics are optional; the data controller and preference controls are explained in the privacy notice.