Loan Calculator

This is a loan calculator application built with Next.js and bootstrapped with create-next-app.

Features

1. Loan Amount Input

   • Allows users to input the loan amount in VND.

2. Loan Term Input

   • Allows users to input the loan term in years (can be fractional).

3. Calculation Method Selection

   • Users can choose between two calculation methods:
     • Annuity (Equal Principal and Interest)
     • Fixed Principal, Reducing Interest

4. Interest Rate Generation

   • Generate interest rates for each year or a common interest rate for all years.

5. Interest Rate Input

   • Allows users to input interest rates for each period.

6. Repayment Schedule Calculation

   • Calculates the repayment schedule based on the input values and selected calculation method.

7. Repayment Schedule Display

   • Displays the repayment schedule in a table format with the following columns:
     • Month
     • Beginning Balance (VND)
     • Interest (VND)
     • Principal (VND)
     • Total Payment (VND)
     • Ending Balance (VND)

8. Statistics Display

   • Displays total interest payable and total principal and interest payable.

9. Repayment Chart

   • Displays a line chart showing the beginning and ending balance over the loan term.

10. Interest and Principal Chart

    • Displays a bar chart showing the interest and principal amounts over the loan term.

11. CSV Download

    • Allows users to download the repayment schedule as a CSV file.

12. Share Plan

    • Allows users to share the repayment plan via a unique link.

13. Multi-language Support

    • Supports English and Vietnamese languages.

14. Error Handling

    • Displays modal messages for invalid inputs such as invalid loan term, loan amount, or interest rates.

15. Compare Methods Side-by-Side

    • Toggle to compare Annuity vs Fixed Principal methods simultaneously.
    • Shows interest difference and which method saves more.

16. Payment Breakdown Chart

    • Doughnut chart showing Principal vs Interest ratio in total payment.

17. Early Repayment Calculator

    • Calculate interest savings from extra payments (one-time or monthly).
    • Shows months reduced from early repayment.

18. Affordability Calculator

    • Input monthly income to calculate maximum loan amount.
    • Based on DTI (Debt-to-Income) ratio: 43% max, 36% comfortable.
    • DTI Threshold Guide:
      • Below 36%: Ideal - Strong financial health
      • 37-42%: Acceptable - Be cautious with new debt
      • 43-49%: Warning - High debt risk, may face loan rejection
      • Above 50%: Critical - Need debt reduction plan urgently

19. Save/Load Plans

    • Save multiple loan plans to localStorage.
    • Load and compare different scenarios.

20. Export to PDF

    • Professional PDF export of repayment schedule.
    • Supports Vietnamese (ASCII-safe) and English.

Documentation

Detailed calculation documentation available in docs/:

Document	Description
Affordability Calculator	How max loan is calculated based on DTI ratio
Early Repayment	How interest savings are calculated

Vietnamese versions: *_vi.md

SEO Optimization

This application includes the following SEO optimizations:

• Meta tags for description, keywords, and author.
• Sitemap XML for better indexing by search engines.
• SEO-friendly URLs.

Getting Started

Prerequisites

Make sure you have the following installed:

• Node.js (version 22 or later)
• pnpm (version 10 or later)

Installation

First, clone the repository:

git clone https://github.com/lamngockhuong/loan-calculator.git
cd loan-calculator

Then, install the dependencies:

pnpm install

Running the Development Server

First, run the development server:

pnpm dev

Open http://localhost:3000 with your browser to see the result.

You can start editing the page by modifying app/page.tsx. The page auto-updates as you edit the file.

Running Tests

To run tests, use the following command:

pnpm test

Building for Production

To create an optimized production build, run:

pnpm build

Learn More

To learn more about Next.js, take a look at the following resources:

• Next.js Documentation - learn about Next.js features and API.
• Learn Next.js - an interactive Next.js tutorial.

You can check out the Next.js GitHub repository - your feedback and contributions are welcome!