French amortization plan

Build a French (annuity) mortgage amortization schedule: fixed monthly installments that each split into interest and principal, with interest declining and principal rising over the loan term. This is the repayment shape used by many European and retail home loans.

Formula

With principal P, annual nominal rate r%, and n monthly payments, the monthly rate is i = r/100/12. The constant installment is

M = P × (i (1+i)^n) / ((1+i)^n − 1)

(or P/n when i = 0). Each month, interest = remaining balance × i, principal = M − interest, and the balance decreases by the principal portion until it reaches zero.

When to use it

• Compare total interest for different rates or terms before talking to a lender
• See how early payments are interest-heavy versus later principal-heavy months
• Produce a month-by-month teaching table for fixed-rate loans

Limitations

Only monthly payment frequency is supported. The model ignores fees, insurance, taxes, variable rates, prepayments, and negative amortization. Rounding in real bank systems can differ by cents. Currency is unitless—interpret numbers in your local currency yourself.

Example

A loan of 200 000 at 3.5% annual interest over 360 months yields a monthly installment of about 898.09, total paid about 323 312, and total interest about 123 312. Early rows show interest larger than principal; later rows reverse that pattern.

This skill is available over A2A JSON-RPC and REST. When you already know the skill id and export, call execute directly—no discovery step required.

REST example

curl -sS -X POST https://toolplaza.app/api/helpers/execute \
  -H 'Content-Type: application/json' \
  -d '{"skillId":"mortgage__french-amortization-plan","export":"calculateFrenchAmortizationPlan","args":[10,20]}'

A2A JSON-RPC example

Send POST https://toolplaza.app/api/a2a with:

{
  "jsonrpc": "2.0",
  "id": "1",
  "method": "message/send",
  "params": {
    "message": {
      "messageId": "uuid",
      "role": "user",
      "parts": [
        {
          "kind": "text",
          "text": "ignored"
        }
      ]
    },
    "metadata": {
      "toolplaza": {
        "skillId": "mortgage__french-amortization-plan",
        "export": "calculateFrenchAmortizationPlan",
        "args": [
          10,
          20
        ]
      }
    }
  }
}

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