ADP provides payroll processing, human resources software and benefits administration services that businesses of nearly every size outsource rather than manage internally. Payroll is a mission-critical, recurring task that companies rarely switch providers for once established, since moving payroll systems carries real operational risk, which gives ADP an unusually sticky, subscription-like revenue base. Beyond core payroll, the company has expanded into broader human capital management software covering hiring, time tracking and benefits, competing with both dedicated HR software vendors and other payroll processors. ADP also earns meaningful interest income on the client funds it temporarily holds between collecting payroll taxes and remitting them to government agencies, which means its earnings get a modest boost when interest rates are higher.