Módulos IRPF
modulosirpf.es
Calculate your IRPF & IVA módulos for free — without sending your data to any server
The free calculator with all 81 Anexo II activities, 4 calculation types, and verification against Orden HAC/1425/2025. Your financial data never leaves your browser.
81
Activities covered
Full Anexo II, Orden HAC/1425/2025
1,956
Unit tests
32 files, all calculation phases
4
Calculator types
IRPF, agricultural, multi-activity, entities
The Challenge
Self-employed workers on módulos face a 4-phase IRPF calculation with incompatibility rules between correction indices. Existing tools are paid, require registration, or send financial data to servers. Official AEAT documentation is dense legal text, not a usable calculator.
The Approach
Step-by-step wizard: select your activity, enter modules, apply corrections, and get phase-by-phase results. Every formula verified against Agencia Tributaria reference values. Complete privacy: zero data transmission, everything runs in your browser.
Architecture
4-phase IRPF calculation pipeline: base yield, incentives, correction indices with incompatibility rules, and blanket reduction
1,956 unit tests across 32 files covering all calculation phases, edge cases, and legal compliance scenarios
100% client-side architecture — zero API calls for financial data, privacy by design
Programmatic SEO: 81 SSG activity pages with structured JSON-LD and dynamic sitemap
Key Technical Decisions
Client-side calculations instead of server: complete privacy, no data liability, works offline
4-phase pipeline mirroring the legal structure: direct maintainability and testability against the regulation
Vitest with 1,956 tests verified against AEAT reference values for IAE codes 642.6 and 672.1
Programmatic SEO for 81 activities: each code gets its own page with modules and data table, capturing long-tail traffic
How It Was Built
Built solo, translating dense legal text (Orden HAC/1425/2025) into a usable calculator. The biggest technical challenge: implementing the 4-phase pipeline with incompatibility rules between correction indices (seasonal + new activity cannot combine, small business + excess cannot combine). The 1,956 tests were built verifying against official AEAT reference values for IAE codes 642.6 and 672.1. Integrates into the fiscal ecosystem alongside conversoriaecnae.es and gestoriascercademi.com.
Results
81 static pages capture long-tail traffic for "módulos [activity name]" searches. Bidirectionally linked with conversoriaecnae.es for mutual topical authority reinforcement. Editorial blog with Sanity CMS covering objective estimation topics. Shared newsletter with the fiscal ecosystem for audience retention.
Tech Stack
What you get
- Your financial data never leaves your browser — 100% client-side calculations
- 4 calculators: standard, agricultural, multi-activity, and entity attribution
- Dynamic forms that adapt to your specific activity modules
- Quarterly fractional payment estimates (Modelos 131/303) included
- 81 activity pages with module breakdowns and CNAE cross-references