A personal finance tracker built around a simple question: how much can I actually spend this month without derailing anything?
Pheidon was a king of Argos in the 7th century BC, credited with the first system of weights and measures in the Greek world. His name comes from the verb pheidomai, to spare or economise.
Greek and English interface, light and dark themes, installable on a phone.
Most expense trackers show you what you spent. Pheidon tries to answer what you can spend next.
A free-to-spend limit that accounts for everything else. Income, minus fixed costs, minus essentials, minus what your goals require, minus a buffer for the unexpected. What remains is genuinely discretionary. Goals are funded before discretionary spending, not from whatever happens to be left over.
Recurring entries that project forward. Declare your rent once and it is both recorded each month and included in every future projection. Declare that a contract ends in February and the forecast for March drops on its own.
Trip mode. On a three-day trip you make twenty small purchases. Picking a category for each one is work nobody does, so in practice nothing gets recorded. Drop a description and an amount into the trip instead; when it closes, everything merges into a single transaction.
Category flexibility drives the logic. Every category is fixed, essential or discretionary, and only discretionary spending counts toward the free-to-spend limit. You can also mark any category as untouchable, and it will never be suggested for a cut regardless of how tight things get.
AI suggestions that never do arithmetic. All figures are computed locally and exactly. A language model receives those finished numbers and writes the interpretation. This is deliberate: a model doing the maths is the surest way to get a confidently wrong figure. Suggestions are validated in code afterwards, so a proposal to cut rent or an untouchable category is discarded before it is shown.
React 18 · TypeScript · Vite · Tailwind CSS v4 · Recharts · Zustand · i18next Supabase for auth and storage · Google Gemini for suggestions · deployed on Vercel
npm install
npm run devRuns at http://localhost:5173 without an account. Data is stored in the
browser. For accounts and sync, see DEPLOYMENT.md.
| Command | Purpose |
|---|---|
npm run dev |
Local development |
npm run build |
Production build in dist/ |
npm run typecheck |
Type checking only |
npm run preview |
Preview the production build |
The codebase separates logic from presentation strictly, so a future React Native port needs only the screens rewritten.
src/
├─ lib/ Pure TypeScript. No React, no DOM. All calculation lives here.
├─ types/ The data model.
├─ features/ Screens, organised by feature rather than by file type.
├─ store/ Storage behind a repository interface: local or Supabase.
└─ i18n/ Greek and English, kept in sync.
api/ Vercel serverless function that talks to Gemini.
supabase/ Schema and row-level security policies.
Amounts are stored as integer minor units, never floats, and the number of decimal places comes from the currency: 100 units in a euro, none in a yen.
See ARCHITECTURE.md for the reasoning behind the structure.
Pheidon is a progressive web app, so it installs from the browser without an app store.
Android — open the site in Chrome, tap the menu, then Install app.
iPhone — open the site in Safari, tap the Share button, then Add to Home Screen. Safari is required: on iOS only Safari can install a web app.
Once installed it runs in its own window without a browser bar and keeps its icon on the home screen. Updates arrive on their own, with no store review.
The app shell is cached, so it opens without a connection, but your data lives in Supabase and needs one to load. Offline entry with later sync is not implemented yet.
Each account sees only its own data. Separation is enforced by row-level security in the database rather than by application code, so it cannot be forgotten in a query.
Only per-category aggregates are sent to the language model: the category key, its average, the current month's total and the trend. Individual transactions, merchant names, notes and email addresses never leave the device.
Working: transactions, categories with custom editing, recurring entries, trips, month navigation with projections, charts, the free-to-spend limit, analysis, auth, Greek and English, light and dark themes.
Implemented but without a UI yet: financial goals and declared income periods. The
logic in lib/goals.ts and lib/forecast.ts is written and tested; only the screens
to enter them are missing.
© 2026 Ioannis Kalaitzidis. All rights reserved.
This repository is public for reference and portfolio purposes. Visible source
is not open source: no permission is granted to copy, modify, deploy or reuse
it. See LICENSE for the full terms.