Summary

Implements firm-level VAT logic for PolicyEngine UK, enabling modeling of VAT at the business level with registration thresholds and rate calculations.

Changes

• ✨ Added Firm entity with owner role linking to persons
• 📊 Created VAT parameters:
  • Registration threshold (£90,000)
  • Deregistration threshold (£88,000)
  • Zero rate (0%)
• 🧮 Implemented 8 VAT calculation variables:
  • firm_turnover: Annual business turnover
  • firm_vat_registered: Registration status based on threshold
  • firm_standard_rated_supplies: Supplies at 20% rate
  • firm_reduced_rated_supplies: Supplies at 5% rate
  • firm_zero_rated_supplies: Supplies at 0% rate
  • firm_vat_on_sales: Output VAT calculation
  • firm_vat_on_purchases: Input VAT
  • firm_net_vat_liability: Net VAT (output - input)

Testing

• ✅ 8 tests passing (3 entity tests, 5 VAT tests)
• 🧪 Tests cover entity creation, VAT thresholds, and calculations
• 🎨 Code formatted with Black

Use Cases

This enables PolicyEngine to:

• Model VAT policy changes on businesses
• Analyze VAT threshold impacts
• Calculate VAT revenue from firms
• Support business tax reform analysis

Fixes #1320

🤖 Generated with Claude Code