About FiscalFold | FiscalFold

FiscalFold is a free, open tool that makes global tax data accessible, transparent, and comparable. We believe everyone deserves to understand how their income is taxed — without jargon, paywalls, or guesswork.

Our Mission

Tax calculations should be deterministic, transparent, and grounded in real data. Too many online tax tools rely on oversimplified estimates or opaque AI. FiscalFold takes a different approach:

Deterministic Math: Every tax figure is computed from official statutory bracket tables stored in our database — never hallucinated by AI.
Cited Sources: Our AI explanations are grounded in IRS Publications, OECD Taxing Wages, and official government tax guides — with page-level citations.
Transparent Methodology: We document exactly how every calculation works in our data methodology page.

What We Cover

5 Countries

United States, United Kingdom, Germany, France, and Spain — with full bracket data, deductions, and social contributions for 2026.

Side-by-Side Comparisons

Compare any two countries at any income level with detailed breakdown of brackets, effective rates, and take-home pay.

AI-Grounded Explanations

Powered by Google Vertex AI with Retrieval Augmented Generation (RAG) — citing specific pages from 18 official government documents.

50 US States

Our "Best Places to Live" tool compares take-home pay across all 50 US states, including state income tax, federal tax, and FICA.

Our Data Sources

FiscalFold's calculations are built on 18 official government documents stored in our data infrastructure:

United States: IRS Revenue Procedure 2025-19, IRS Publication 15-T
United Kingdom: HMRC Income Tax rates and allowances
Germany: Bundesfinanzministerium Einkommensteuer-Tarif
France: Direction generale des finances publiques bareme IR
Spain: Agencia Tributaria IRPF tarifa estatal
OECD: OECD Taxing Wages 2024 and Tax Database

For complete documentation of our methodology, see our Data & Methodology page.

Technology

FiscalFold is built with modern, production-grade technologies:

Frontend: Astro + React with Tailwind CSS, deployed on Cloudflare Pages
Backend: Spring Boot 3 / Java 21 REST API with Redis caching
Database: PostgreSQL with official government tax tables
AI: Google Vertex AI with Data Store (RAG) for grounded explanations
Security: API key authentication, IP-based rate limiting, CORS restrictions

Important Disclaimer

FiscalFold provides tax calculations for informational and educational purposes only. Our calculations are estimates based on statutory rates and standard deductions. They do not account for all credits, exemptions, local surcharges, or individual circumstances. Always consult a qualified tax professional for advice specific to your situation.

Get in Touch

Have questions, feedback, or data corrections? Contact us at hello@fiscalfold.app. We take data accuracy seriously and welcome corrections backed by official source documents.