AI Financial Calculator

Author: Trygve "Trig" Bundgaard (aka Ubuntu Buddha)

A production-style WordPress plugin demonstrating financial calculations with AI-powered assistance. Built as a portfolio project showcasing OpenAI API integration, complex financial modeling, and interactive user interfaces in a WordPress environment.

Design Philosophy

This plugin showcases production-ready WordPress development with modern patterns:

• AI Integration: Seamless OpenAI API integration with context-aware responses
• Financial Domain Knowledge: Real-world amortization, ROI calculations, and multi-lender comparisons
• Interactive UX: Real-time calculations, form state persistence, and conversational AI
• WordPress Best Practices: REST API endpoints, shortcodes, proper sanitization, and security

Why This Exists

Financial calculators require:

• Complex mathematical calculations (amortization, interest rate modeling)
• Multi-criteria decision making (credit scores, down payments, terms)
• Revenue/profit projections with multiple variables
• User-friendly interfaces that guide decision-making
• AI assistance for personalized recommendations

This plugin demonstrates how to build such a system with WordPress, integrating external AI APIs while maintaining security and performance.

Architecture

graph TB
    A[WordPress Shortcode] -->|Renders| B[Form Template]
    B -->|Submits| C[Form Processor]
    C -->|Calls| D[Loan Calculator]
    C -->|Calls| E[Revenue Calculator]
    C -->|Calls| F[Lender Calculators]
    C -->|Returns| B
    B -->|Displays| G[Results Section]
    G -->|User Query| H[AI Chat Interface]
    H -->|POST| I[REST API Endpoint]
    I -->|Calls| J[OpenAI API]
    J -->|Returns| I
    I -->|JSON| H
    H -->|Renders| K[Markdown Response]

    style I fill:#e1f5ff
    style J fill:#fff4e1
    style C fill:#ffe1e1
    style H fill:#e1ffe1

Core Components

1. Financial Calculators (includes/)

   • Loan amortization with configurable interest rates
   • Revenue/profit projections with expense modeling
   • Multi-lender payment comparisons
   • ROI and payback period calculations

2. AI Integration (includes/chat-endpoint.php)

   • WordPress REST API endpoint
   • OpenAI GPT-4o-mini integration
   • Context-aware system prompts
   • Form data injection for personalized responses

3. Frontend (assets/)

   • Vanilla JavaScript (no framework dependencies)
   • localStorage for form persistence
   • Markdown rendering for AI responses
   • Responsive design with CSS Grid

4. Form Processing (includes/form-processor.php)

   • Multi-criteria interest rate calculation
   • Fee calculations (origination, documentation, servicing)
   • Revenue/expense aggregation
   • Loan repayment simulation

Key Features

Financial Calculations

• Amortization: Standard loan payment calculations with extra payment support
• Interest Rate Modeling: Multi-factor interest rate calculation based on:
  • Credit score ranges
  • Down payment percentages
  • Loan terms
  • Business experience
  • Risk factors (age verification, credit penalties)
• Revenue Projections: Daily/monthly/yearly profit calculations
• Expense Modeling: Spoilage, credit card processing, commissions, operating expenses

AI Assistant

• Context-Aware: Receives full form data and calculation results
• Personalized Recommendations: Analyzes user's financial situation
• Markdown Support: Rich text responses with formatting
• Error Handling: Graceful degradation if API unavailable

User Experience

• Form Persistence: Saves form state to localStorage
• Real-Time Calculations: Instant results on form submission
• Multi-Lender Comparison: Side-by-side payment options
• Data Export: Copy inputs and results to clipboard

Installation

Prerequisites

• WordPress 5.0+
• PHP 7.4+
• OpenAI API key (optional, for AI features)

Setup

1. Install the plugin:

   # Copy the plugin directory to wp-content/plugins/
   cp -r ai-financial-calculator /path/to/wordpress/wp-content/plugins/

2. Activate the plugin in WordPress admin

3. Configure OpenAI API key (optional):

   // In wp-config.php
   define('OPENAI_API_KEY', 'your-api-key-here');

   Or set environment variable:

   export OPENAI_API_KEY=your-api-key-here

4. Add the shortcode to any page or post:

   [ai_financial_calculator]

Configuration

Interest Rate Parameters

Filter hooks allow customization of interest rate calculations:

// Base rate (default: 7.5%)
add_filter('ai_calculator_base_rate', function() { return 8.0; });

// Lender margin (default: 1.5%)
add_filter('ai_calculator_lender_margin', function() { return 2.0; });

// Minimum profit margin (default: 5.0%)
add_filter('ai_calculator_min_profit', function() { return 6.0; });

Lender Payment Factors

Customize alternative lender payment calculations:

// Lender 1 payment factors
add_filter('ai_lender1_payment_factors', function() {
    return [
        12 => 0.08333,
        24 => 0.05394,
        36 => 0.03913,
        48 => 0.03183
    ];
});

// Lender 2 base payments (for $10k loan)
add_filter('ai_lender2_base_payments', function() {
    return [
        12 => 850.00,
        24 => 569.21,
        30 => 432.24,
        36 => 427.97,
        42 => 390.41
    ];
});

Qualification Criteria

// Minimum credit score (default: 650)
add_filter('ai_calculator_min_credit_score', function() { return 700; });

// Allowed loan terms (default: [2, 3])
add_filter('ai_calculator_allowed_terms', function() { return [2, 3, 4]; });

Usage

Basic Calculator

1. Fill in business information
2. Enter loan amount and term
3. Set credit score and other criteria
4. Add product information for revenue calculations
5. Click "Calculate & Get Results"

AI Assistant

After calculating results:

1. Scroll to the AI chat section
2. Ask questions about your results
3. Get personalized recommendations
4. Explore different scenarios

Example queries:

• "What's the best option for my situation?"
• "How can I pay off the loan faster?"
• "What if I increase my down payment to 50%?"
• "Analyze my profit margins"

Technical Details

REST API Endpoint

POST /wp-json/ai-financial-calculator/v1/chat-query
Content-Type: application/json

{
  "prompt": "User's question",
  "form_context": "JSON string of form data and results"
}

Data Flow

1. Form Submission: POST to same page
2. Processing: form-processor.php calculates all values
3. Display: Results rendered in template
4. AI Query: JavaScript sends form context + user prompt
5. Response: OpenAI returns formatted markdown
6. Rendering: Marked.js renders markdown to HTML

Security

• All inputs sanitized with WordPress functions (sanitize_text_field(), wp_kses_post())
• API key stored in environment/config (never in code)
• REST API permission callback with optional nonce verification
• Rate limiting: Per-IP request throttling (configurable via ai_calculator_rate_limit filter)
• SQL injection prevented (no direct DB queries)
• XSS protection via esc_html(), esc_attr(), esc_url()
• Prompt injection mitigation via input sanitization and system prompt isolation

Performance Considerations

• Form State: localStorage reduces server load
• API Calls: Only on user request (not automatic)
• Caching: Results can be cached per session
• Markdown: Client-side rendering (marked.js CDN)

When NOT to Use This

This plugin is not suitable for:

• ❌ Regulated financial services without compliance review and security audit
• ❌ High-traffic production sites without load testing and caching strategy
• ❌ WordPress multisite without namespace isolation testing
• ❌ Environments requiring PCI-DSS compliance without additional hardening

This is a portfolio project demonstrating technical capabilities. For production financial services, additional security hardening, compliance review, and legal consultation are required.

Portfolio Highlights

Skill Demonstrated	Evidence
WordPress Plugin Development	REST API, shortcodes, hooks, proper architecture
AI API Integration	OpenAI integration with context injection
Financial Domain Knowledge	Amortization, interest calculations, ROI modeling
Full-Stack Development	PHP backend + JavaScript frontend + AI middleware
User Experience Design	Form persistence, real-time feedback, conversational UI
Security Best Practices	Input sanitization, API key management, XSS prevention

Dependencies

• WordPress: Core functionality
• OpenAI API: For AI assistant (optional)
• Marked.js: Markdown rendering (loaded via CDN)

License

MIT License - See LICENSE file for details.

Disclaimer

This software is for demonstration purposes only. Financial calculations are simplified models and should not be used for actual lending decisions without professional financial advice. The developers are not responsible for any financial decisions made using this software.

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Built to demonstrate production WordPress development with AI integration. 🚀