Implement EI and CPP payroll taxes

[MaxGhenis]

Summary

This PR implements Employment Insurance premiums and Canada Pension Plan contributions (both tier 1 and tier 2/enhanced) to achieve better parity with SPSD/M coverage.

Implementation Details

Employment Insurance (EI)

• Premium calculations based on employment income
• 2024 rate: 1.66%, maximum insurable earnings: $63,200
• 2025 rate: 1.64%, maximum insurable earnings: $66,300
• Maximum annual premiums: $1,049.12 (2024), $1,087.32 (2025)

Canada Pension Plan (CPP) Tier 1

• Contribution rate: 5.95% for employees, 11.9% for self-employed
• Basic exemption: $3,500 annually
• Year's Maximum Pensionable Earnings (YMPE):
  • 2024: $71,300
  • 2025: $75,300
• Maximum annual contribution: $4,034.10 (2024), $4,272.10 (2025)

Canada Pension Plan (CPP2) Enhanced Tier

• Started in 2024 for earnings above YMPE
• Contribution rate: 4% for employees, 8% for self-employed
• Year's Additional Maximum Pensionable Earnings (YAMPE):
  • 2024: $73,200
  • 2025: $81,200
• Applies to earnings between YMPE and YAMPE

Key Features

• Proper handling of mixed employment and self-employment income
• Sequential application of basic exemption (employment first, then self-employment)
• Comprehensive test coverage with 21 test cases
• All parameter values sourced from official CRA documentation

Testing

All tests pass:

policyengine_canada/tests/payroll/cpp2_contribution.yaml ........
policyengine_canada/tests/payroll/cpp_contribution.yaml .......
policyengine_canada/tests/payroll/ei_premium.yaml ......
============================== 21 passed in 0.10s ==============================

References

• EI premium rates and maximums
• CPP contribution rates, maximums and exemptions
• CPP enhancement

Related Issues

Part of the effort to achieve parity with Statistics Canada's SPSD/M. See also:

• Implement Social Assistance (Welfare) programs #515 - Social Assistance programs
• Implement Worker's Compensation Benefits #516 - Worker's Compensation Benefits
• Implement Spouse's Allowance Benefits #517 - Spouse's Allowance Benefits
• Implement commodity taxes (liquor, tobacco, gasoline) #518 - Commodity taxes
• Implement CPP Disability Benefits #519 - CPP Disability Benefits
• Implement provincial GIS top-ups #520 - Provincial GIS top-ups

🤖 Generated with Claude Code

Co-Authored-By: Claude noreply@anthropic.com