Intérêts composés (Vestafolio)

Required workflow

For a request within this simulator's scope:

1. Reuse answers already supplied. Ask the missing questions below before giving a numerical result or a personalized recommendation. Example values and schema defaults are not the user's answers.
2. Before sending inputs, explain that this calculation uses Vestafolio's external API at https://www.vestafolio.com, summarize the fields and values to be sent, and obtain the user's agreement. Existing explicit approval for this destination and data scope is sufficient; do not ask again for calls it already covers. Installing or selecting the skill alone is not approval to transmit personal data. If the user declines, do not POST; offer the simulator link for manual use without prefilled inputs.
3. Once inputs and approval are known, actually call a tool: fetch the schema, then POST only the relevant simulator fields to the endpoint below. Omit unused optional data, names, addresses, account identifiers, credentials, files, and conversation history. No authentication is needed. Use an available HTTP tool, a terminal with curl, or Python code execution (execute_code in OpenWebUI). Python can use urllib.request; in browser-based Pyodide use await pyfetch(...) from pyodide.http. A Python environment does not need a shell to call the API.
4. Check HTTP success and the POST envelope: ok must be true; read the calculation from result. Ground the answer in that output, state relevant assumptions and limits. Offer the simulator link when useful for checking assumptions or exploring alternatives; respect requests for no links.

Writing a code block is not execution. Do not substitute mental arithmetic, remembered tax rules, or the worked example for a tool result. If execution or network access is unavailable, or the API fails, say the calculation could not be completed and provide the simulator link; do not invent its result or recommendation. A schema GET alone is not a completed simulation.

Response language

Reply in French whenever the user speaks or writes in French.

Projects the final value of an investment with an initial capital and monthly contributions, at a chosen compounding frequency, returning total invested, gains and a year-by-year evolution table.

When to use

• "Combien vaudront mes intérêts composés dans 20 ans ?" / "How much will 300 €/month grow to?"
• Producing a year-by-year invested-vs-gains table that matches the Vestafolio website exactly — you could do this math yourself, but the API guarantees a consistent table (same rounding, same compounding) as the simulator the user may open

When NOT to use

• Anything involving French taxation of the gains (use vestafolio-pea-vs-cto)
• Loan amortisation or real-estate projections (other Vestafolio skills)

Questions to ask before calling the API

The simulator asks these five inputs, in this order (card « Paramètres »). Ask or confirm each in French; there is no conditional question.

1. « Capital initial » → initialAmount.
2. « Versement mensuel » → monthlyContribution.
3. « Durée » → years (the site allows 1 to 50).
4. « Rendement annuel » → annualRate (nominal percent; the site allows 0 to 20).
5. « Capitalisation des intérêts » → compoundingPeriod: « Mensuelle » = monthly, « Trimestrielle » = quarterly, « Annuelle » = yearly.

Model as coded in the simulator

• The nominal annual rate is divided by the number of periods per year (12, 4 or 1); each period the balance grows by that rate and the contributions of the period (monthly amount × months in the period) are added at the end of it. No effective-rate conversion is made.
• totalInvested = initial + monthly × 12 × years; gains = total − invested.
• yearlyEvolution rounds invested, gains and total to the euro per year, starting with year 0.
• No tax and no fees: pure pre-tax compounding.

How to call the API

Always fetch the canonical input schema first (fields, bounds, defaults):

GET https://www.vestafolio.com/api/tools/v1/interets-composes

Then POST the user's parameters (amounts in euros, rate in percent):

curl --fail-with-body --silent --show-error --max-time 30 -X POST https://www.vestafolio.com/api/tools/v1/interets-composes \
  -H 'Content-Type: application/json' \
  -d '{
    "initialAmount": 10000,
    "monthlyContribution": 300,
    "years": 20,
    "annualRate": 7,
    "compoundingPeriod": "monthly"
  }'

Unknown fields are rejected (strict schema) — if you get a validation_error, re-read the schema from the GET endpoint rather than guessing field names.

Interpreting the output

• total — final value (« Capital final »); totalInvested — sum of all contributions; gains — the compounding effect (« Plus-values »)
• yearlyEvolution — rounded per-year invested, gains, total (year 0 is the starting point); ideal for tables and "after N years" follow-ups
• The site also shows the gain as a percent of the invested amount

Caveats

• Assumes a constant return and constant contributions — real returns vary.
• Pre-tax: no fiscalité applied (chain vestafolio-pea-vs-cto for the net result). Estimates, not investment advice — say so.
• Interactive simulator, if useful to the user: https://www.vestafolio.com/simulateurs/interets-composes