Payroll processing software is the backbone of HR operations. It takes employee timesheets, calculates gross pay, deducts taxes and benefits, and delivers net pay on payday. Modern payroll systems are cloud-based, integrated with accounting, and compliant with tax regulations across multiple jurisdictions. As a developer, you're either building payroll systems or integrating with them. The math looks simple (hours × rate - taxes) but regulatory complexity is enormous: tax brackets change annually, national insurance thresholds vary by income, pension rules shift, and compliance failures trigger HMRC penalties.