Renovation Loan Simulator (France)

A desktop app (Qt / PySide6) to simulate a loan for renovating an apartment in France (prêt travaux).

Install

pip install loan-simu
loan-simu            # or: python -m loan_simu

It needs Python 3.10 or later. PySide6 and matplotlib are installed with it.

Numbers are shown in French format and you can type 4,5 or 4.5. Results update as you type.

The app follows the system's light or dark mode. To force one, set LOAN_SIMU_THEME=light or LOAN_SIMU_THEME=dark.

Simple mode

You enter the works cost, down payment, duration, rate, insurance, your net monthly income and your other loan payments. You get:

• the monthly payment, the total cost of credit and the APR (TAEG)
• the debt ratio (taux d'endettement), on a gauge against the 35 % HCSF limit, and the money left each month
• a breakdown of capital, interest and insurance
• a table comparing durations from 3 to 25 years, with the debt ratio for each; click a row to use that duration

In-depth mode

The in-depth mode also has an amortization table (combined or per loan, by month or by year, exported as CSV for French Excel) and charts.

Calculation rules

• Monthly rate = nominal rate / 12 (taux proportionnel), constant monthly payments.
• The TAEG is the actuarial rate including interest, insurance and upfront fees. It is calculated without the early repayment, as banks do.
• IRA:
  • real-estate loan: the lower of 6 months of interest and 3 % of the remaining capital
  • consumer loan: 1 % of the amount repaid (0.5 % if 12 months or less remain), nothing for 10 000 € or less, capped at the remaining interest
  • éco-PTZ: no penalty

Keep these up to date

The values in src/loan_simu/core.py change over time:

• Usury rates (USURY_*) are published every quarter by the Banque de France. The real-estate table is from Q4 2026. The consumer table is from Q3 2026, because the Q4 figures were not found.
• Éco-PTZ caps (ECO_PTZ_CATEGORIES): check them on service-public.fr (page F19905).

Development

git clone https://github.com/leoguignard/loan-simu.git
cd loan-simu
pip install -e ".[dev]"  # app + release tools (bumpver, build, twine)
python -m unittest       # engine tests + offscreen UI smoke test

src/loan_simu/
  core.py         calculation engine (no GUI dependency)
  ui/
    app.py        main window and entry point
    simple.py     simple mode
    advanced.py   in-depth mode
    widgets.py    cards, number fields, debt-ratio gauge
    charts.py     matplotlib charts
    theme.py      light/dark palettes and stylesheet
tests/            engine tests and an offscreen UI smoke test

Releasing to PyPI

1. Bump the version with bumpver. It updates pyproject.toml and src/loan_simu/__init__.py, then commits and tags (needs a clean working tree):

   bumpver update --patch --dry   # preview the change
   bumpver update --patch         # or --minor / --major
   git push --follow-tags
   

2. Build and check:

   rm -rf dist && python -m build
   twine check dist/*
   

3. Upload to TestPyPI first, then to PyPI:

   twine upload --repository testpypi dist/*
   twine upload dist/*
   

Disclaimer

This is a simulation, not a loan offer. Your bank's offer (offre de prêt) and its FISE are the documents that count.

License

MIT, see LICENSE.