Fight for SMB system of record

This is a fight over who becomes the small business system of record for money and people. ADP starts with scale and breadth, serving more than 940,000 small businesses through RUN and bundling payroll, tax filing, benefits, retirement, and HR. Gusto wins by making that same bundle feel simpler for a 10 person company, while Mercury is attacking from the banking side by turning payroll into one more workflow inside the company bank account.1 2 3 4 5 6

• ADP is the incumbent because payroll is only the entry point. Once a business runs payroll there, ADP can also sell benefits, retirement, compliance, workforce management, and even a co employment model through TotalSource, which makes switching harder as the company grows.1 2 5
• Mercury Payroll is a new kind of competitor because it comes from the treasury layer, not the HR layer. Mercury bought Central in October 2025, adding payroll, benefits, PTO, HR, and state compliance to a banking product already used by startups to hold cash, pay vendors, and separate operating and payroll accounts.3 4 6
• Gusto sits between those models. It already bundles payroll with 401(k) and benefits, and its edge is that deductions, contributions, and filings run automatically off the paycheck flow. That makes every added product easier to adopt than if payroll, retirement, and banking all live in separate systems.5 6 7

The market is moving toward fewer back office systems, not more. ADP will keep defending its installed base with breadth and retention, Mercury will keep pulling startup banking customers into payroll, and Gusto will keep expanding wallet share by making payroll the hub that powers the rest of the SMB back office.1 2 3 5 6