Our Data & Methodology
Transparency is foundational to FiscalFold. Every tax figure on this platform is deterministic — computed from official statutory rates, not generated by AI. Here's exactly how it works.
Two-Path Architecture
Path A: Deterministic Math
All tax calculations are performed by a Java engine that applies statutory bracket rates stored in our PostgreSQL database. The math is deterministic — the same input always produces the same output. No AI is involved in computing any tax figure.
Path B: AI-Grounded Context
Contextual explanations (like "why is Spain's effective rate higher?") are generated by Vertex AI Search, which reads official IRS/OECD/government PDFs and provides answers with page-level citations. The AI never generates tax numbers.
Our Data Sources
Spain
- Agencia Tributaria — Manual de la Renta 2024 (Parts 1 & 2)
- OECD TaxBEN — Spain Country Report
Germany
- BMF — Einkommensteuer Grundtabelle 2026
- OECD TaxBEN — Germany Country Report
Note: Germany uses continuous tax formulas. Brackets shown are simplified approximations. See the BMF calculator for precise amounts.
United Kingdom
- HMRC CWG2 (2025-26) — Rates & Thresholds for Employers
- OECD TaxBEN — United Kingdom Country Report
France
- DGFiP — Brochure Pratique Impôt sur le Revenu 2025
- OECD TaxBEN — France Country Report
OECD Global Data
- OECD Taxing Wages — International Tax Data
- OECD TaxBEN — Tax-Benefit Country Reports (Methodology Manual + Glossary)
Calculation Methodology
1. Tax Bracket Application
Income is taxed progressively — each portion of income is taxed at the rate for that bracket. For example, a US single filer earning $60,000 pays 10% on the first $12,400, 12% on income from $12,400 to $50,300, and 22% on the remainder. The effective rate is always lower than the marginal rate.
2. Standard Deductions
Each country's standard deduction or personal allowance is applied before bracket calculation. For example, the US standard deduction for 2026 is $15,000 (single), Germany's Grundfreibetrag is €12,096, and the UK personal allowance is £12,570.
3. Social Contributions
Employee-side social security contributions (FICA in the US, NICs in the UK, etc.) are calculated separately and shown alongside income tax for a complete picture of your total tax burden.
4. AI Explanations
When you compare countries, Vertex AI Search reads our collection of 18 official government PDFs and OECD reports to generate explanations. Every AI-generated statement includes citations to specific documents so you can verify the claims yourself.
Limitations & Disclaimers
- ! FiscalFold provides estimates only. These are not tax filings and do not constitute tax advice.
- ! Regional/state/municipal taxes are not included (e.g., US state taxes, Spanish autonomous community surcharges).
- ! Germany uses continuous formulas, not flat brackets. Our bracket approximation may differ slightly from precise amounts.
- ! Only standard deductions are applied. Itemized deductions, credits, and special exemptions are not computed.
- ! Always consult a licensed tax professional before making financial decisions based on these calculations.
Data Update Schedule
February 14, 2026
2026 (all countries)
Annual (when new rates are published)
18 official source documents