How I built a desktop budgeting app with Flask, SQLite, and Chart.js

cattail — Fri, 05 Jun 2026 13:03:18 +0000

I'm a finance student, not a CS major. Last year, I realized I was paying $180 annually to a budgeting app. So I decided to build my own. Here's how it went.

Why a Desktop App?

I wanted three things:

No cloud. My financial data stays on my machine.
No subscription. Pay once, use forever.
No setup. Double-click and it works.

A local web app (Flask + browser) checked all three boxes.

The Stack

Layer	Technology
Backend	Python + Flask
Database	SQLite
Frontend	HTML, CSS, vanilla JavaScript
Charts	Chart.js
Packaging	PyInstaller

I chose Flask because it's lightweight. SQLite because it's zero-config. Chart.js because it looks great out of the box.

What the App Does

Monthly budget with auto-generated bar and pie charts
Daily transaction tracking with keyword-based category matching
Multi-currency support with real-time exchange rate preview
Savings goals with progress bars and milestone celebrations
Subscription manager with billing countdowns
Debt payoff comparison (Snowball vs Avalanche)
Asset and liability tracking for net worth overview
Full bilingual support (English and Chinese)

The Architecture

The app runs a local Flask server. On startup, it opens the user's browser automatically. All data lives in a single database.db file next to the executable.

Here's a simplified view of the project structure:

budget_tracker/
├── app.py
├── models.py
├── routes.py
├── templates/
│ ├── base.html
│ ├── index.html (dashboard)
│ ├── budget.html
│ ├── transactions.html
│ ├── annual.html
│ ├── savings.html
│ ├── subscriptions.html
│ ├── debt.html
│ ├── assets.html
│ └── settings.html
├── static/
│ ├── css/style.css
│ └── js/
│ ├── charts.js
│ └── app.js
└── database.db

Key Design Decisions

1. Keyword Auto-Categorization

Users can set rules in Settings. Type "Starbucks" in the note field, and the category auto-fills to "Food." This is done with a simple dictionary lookup, no AI required.

2. Multi-Currency Handling

The Settings page stores exchange rates. When a user logs a transaction in EUR, the app converts it to their base currency (e.g., USD) in real time. The converted value is stored in a separate base_amount column.

3. Proactive Alerts

The dashboard auto-refreshes every 30 seconds via AJAX. If a budget category exceeds 80%, the card turns red. If a subscription bill is due within 7 days, it shows a countdown. No user action needed.

Packaging with PyInstaller

The final step was turning the Python project into a single .exe file:

pyinstaller --onefile --add-data "templates;templates" --add-data "static;static" app.py

The output is about 21 MB. Users download, unzip, double-click, and their browser opens automatically. No Python, no pip, no terminal.

What I Learned

Start simple. My first version was just a budget table and a transaction log. I added features one by one based on my own needs.
SQLite is enough. For a local single-user app, you don't need PostgreSQL.
Chart.js is wonderful. Responsive, customizable, and the CDN link is all you need.
Ship before you feel ready. I wanted to add bank sync and a mobile app. Instead, I launched with what I had. Glad I did.

Try It

Fortune Desk is available on itch.io for a one-time purchase. No subscription, no cloud, no accounts.

If you're a developer thinking about building your own tool — do it. The skills you gain are worth more than any app you'll replace.

DEV Community: cattail