RealEstimate: Real Estate Calculator

A FastAPI-based web application for real estate calculations, providing a user-friendly interface for mortgage payment calculations and rent vs. buy comparisons.

Table of Contents

• Project Structure
• Setup
• Running the Application
• Features
• Calculation Logic

Project Structure

.
├── LICENSE
├── Readme.md
├── app.py
├── calculations
│   ├── comparison.py
│   └── mortgage_calculations.py
├── main.py
├── realEstimate.py
├── requirements.txt
└── templates
   ├── index.html
   └── results.html

Setup

1. Clone the repository:

     git clone <repository-url>
   

2. Navigate to the project directory:

     cd <project-directory>
   

3. Create a virtual environment:

     python3 -m venv venv
   

4. Activate the virtual environment:

   • On Windows:

     venv\Scripts\activate
   

   • On Unix or MacOS:

     source venv/bin/activate
   

5. Install the required packages:

     pip install -r requirements.txt
   

Running the Application

To run the application, use the following command:

python app.py

This will start a development server on http://localhost:5000.

Features

1. User-friendly Web Interface: Input mortgage parameters through a clean, responsive HTML form.
2. Mortgage Payment Calculation: Calculates monthly mortgage payments for both fixed and variable interest rate periods.
3. Rent vs. Buy Comparison: Provides a detailed month-by-month comparison of costs associated with renting versus buying.
4. Comprehensive Results: Displays total principal paid, total interest paid (min and max), total rent and savings paid, and overall financial differences.

Calculation Logic

This API uses the loan amortization formula to calculate monthly mortgage payments. The formula is as follows:

$$M = P[r(1+r)^n]/[(1+r)^n – 1]$$

Where:

• M is your monthly payment.
• P is the principal loan amount.
• r is your monthly interest rate, calculated by dividing your annual interest rate by 12.
• n is your number of payments (the number of months you will be paying the loan).

The application uses the following key calculations:

1. Monthly Mortgage Payment: Calculated using the standard amortization formula.

2. Total Principal Paid: Sum of all principal payments over the loan term.

3. Total Interest Paid: Sum of all interest payments, with minimum and maximum values based on variable interest rates.

4. Total Rent and Savings Paid: Sum of monthly rent payments plus potential principal payments if buying.

5. Financial Difference: Comparison between total costs of buying versus renting, including percentage differences.

The results are presented in both summary and detailed month-by-month formats, allowing users to make informed decisions about renting versus buying property.

For more detailed information about the calculations, please refer to the calculations directory in the source code.

Inspired by: https://www.rumah123.com/kpr/simulasi-kpr/

API Endpoints

Calculate Mortgage Payments

Calculate monthly mortgage payments based on given parameters.

• URL: /calculate_mortgage_payments
• Method: POST
• Data Params:

    {
      "property_price": 300000,
      "down_payment_percentage": 20,
      "interest_rate_first_period": 3.5,
      "interest_rate_subsequent_min": 3.0,
      "interest_rate_subsequent_max": 4.0,
      "mortgage_term_years": 30,
      "fixed_interest_duration_years": 5
    }
  

• Success Response:
  • Code: 200
  • Content:

    {
      "monthly_payment_first_period": 1077.71,
      "monthly_payment_subsequent_min": 1010.92,
      "monthly_payment_subsequent_max": 1145.80
    }
  

Month by Month Comparison

Perform a month-by-month comparison of mortgage costs versus renting.

• URL: /month_by_month_comparison
• Method: POST
• Data Params:

    {
      "monthly_payment_first_period": 1077.71,
      "monthly_payment_subsequent_min": 1010.92,
      "monthly_payment_subsequent_max": 1145.80,
      "monthly_rent": 1200,
      "mortgage_term_years": 30,
      "loan_amount": 240000,
      "interest_rate_first_period": 3.5,
      "interest_rate_subsequent_min": 3.0,
      "interest_rate_subsequent_max": 4.0,
      "fixed_interest_duration_years": 5
    }
  

• Success Response:
  • Code: 200
  • Content:

    {
      "comparison": [
        {
          "month": 1,
          "mortgage_payment": 1077.71,
          "rent_payment": 1200,
          "principal_paid": 352.71,
          "interest_paid": 725.00,
          "cumulative_principal_paid": 352.71,
          "cumulative_interest_paid": 725.00,
          "remaining_loan_balance": 239647.29
        },
        // ... (data for subsequent months)
      ]
    }