Mortgage calculator tool for Netherlands

---

features:

• Minimalistic design:
  • virtually no dependencies.
  • no need to install anything for local testing / development.
• Superflexible, yet to get started you only need to provide a handful of figures.
• Supports 3 most popular mortgage types in Netherlands: "Annuity", "Linear" and "Interest-only".
• Adjustable additional periodic extra repayment schedules, monthly, flexible periodic repayments:
  • ability to "program" a monthly additional repayment.
  • 3 additional periodic repayments with any periodicity and starting month.
• Adjustable in-place extra repayments (click on any cell in "extra_payment" column in the "Payments schedule"):
  • for already calculated payment schedule you can "change" any extra repayment in-place and the schedule will be recalculated from that month onward.
• Renting, income parameters for assets ROI modelling:
  • takes into account deposit rate, house market growth rate, salary and renting information to calculate monthly total assets state and final "ROI" figures.
• What-if modellig provides uni- and bi-parameter mortgage modelling functionality:
  • to test different loan parameters and to find the most convenient/profitable mortgage configuration.
• Entrypoint modelling:
  • comparison of financial outcomes for "buy now" vs "buy X months later" scenarios.
• LLM assistant:
  • a small language model integrated with calculator. Works directly in the browser and can set mortgage calculation parameters, interpret calculation results and answer general mortgage-related questions.
• Mortgage / financial context fine-tuning:
  • approximately 30 parameters available to describe the financial context.

---

"What-if" modelling:

Allows to model the mortgage as a function of a parameter(s).

• Any adjustable mortgage parameter can be "probed" on a range of values (e.g. extra monthly repayment).
  • you'll see the parameter variable name when you hover mouse over the input field for it
• Resulting output parameters of the mortgage then plotted on the graph (e.g. actual mortgage term).

Allows bi-parametric mortgage modelling.

• With two parameters being "tested" - target metric drawn on a 3-D surface plot (e.g. actual mortgage term as a function of both extra monthly repayment and initial downpayment).

---

AI assistant:

---

hosted on github pages:

• English: Mortgage calculator tool (Netherlands)
• Dutch: Hypotheek berekenen

---

Local development / testing:

1. clone the repo: git clone https://github.com/r0d1on/mortgage-tool
2. make changes
3. open ./en/mortgage-calculator.html in your browser

---

How to contribute:

All contributions you make are highly appreciated.

Add changes, open a pull request

1. Fork the Project
2. Create your Feature Branch (git checkout -b feature/new-amazing-parameter)
3. Commit your Changes (git commit -m 'added new loan parameter')
4. Push to the Branch (git push origin feature/new-amazing-parameter)
5. Open a Pull Request

---

credits:

• uses https://github.com/plotly/plotly.js for visualisation
• inspired by https://github.com/santiago-pan/mortgage-calculator
• COOP/COEP workaround for Github pages: https://github.com/gzuidhof/coi-serviceworker
• wllama - Wasm binding for llama.cpp: https://github.com/ngxson/wllama
• Phi-3-mini LLM model: https://huggingface.co/microsoft/Phi-3-mini-128k-instruct (MIT license)

---

support:

• buymeacoffee.com/r0d1on
• patreon.com/r0d1on