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# Loan Calculator

## /loan-calculator

This endpoint calculates the monthly payment for a loan based on the provided loan amount, annual interest rate, and duration in years. It accepts a POST request with form data including the `loanAmount`, `annualInterestRate`, and `durationYears`. If any of the provided values are not valid numeric values, it returns a 400 error with a corresponding message. If the calculation results in a valid monthly payment, it returns the monthly payment rounded to 2 decimal places. If the calculation is invalid, it returns a 400 error with a corresponding message.

**Headers**:

* `Content-Type`: `application/x-www-form-urlencoded`

**Request Body (loanAmount, annualInterestRate, durationYears)**

Form Data:

* `loanAmount`: The amount of the loan.
* `annualInterestRate`: The annual interest rate (in percentage).
* `durationYears`: The duration of the loan in years.

**Example**:

```plaintext
loanAmount: 10000
annualInterestRate: 5
durationYears: 3
```

**Response**\
Upon successful calculation, the endpoint responds with the monthly payment amount.

**Example**:

```json
{
    "monthlyPayment": "299.71"
}
```

**Error Responses**

* **Status Code: 400 Bad Request**

  **Body**: `"Please provide valid numeric values for loan amount, interest rate, and duration."`

  **Description**: Occurs if any of the parameters are missing or not a valid number.
* **Status Code: 400 Bad Request**

  **Body**: `"Invalid calculation. Please check the input values."`

  **Description**: Occurs if the calculation cannot be completed due to invalid input values, such as an interest rate of 0% over a 0 year duration, which are not mathematically viable for the formula.

This endpoint allows for a quick calculation of the monthly payments required for a loan based on the principal amount, the interest rate, and the loan duration. The calculation assumes that payments are made monthly and that the interest is compounded monthly as well.