The core structural difference, in one sentence.
A payroll company is a vendor — you remain the employer, they process the math. A PEO is a co-employer — you and the PEO share legal employment responsibility, which unlocks economies of scale on benefits, compliance, and risk but reshapes who's liable for what.
Everything else — pricing, technology, service depth — derives from this distinction. If you don't understand it, the rest of the comparison won't make sense.
Co-employment, explained.
Under a PEO arrangement, your employees become the joint employees of both your business and the PEO. The PEO becomes the employer of record for payroll tax filings, benefits administration, and certain compliance obligations. You retain operational control — hiring, firing, day-to-day management, business strategy. The PEO retains the administrative employer functions.
The economic logic is straightforward: by pooling your employees with thousands of other small employers under their EIN, the PEO accesses pricing and benefits leverage that's structurally unavailable to a 25-person business operating alone. The trade is that you've added a co-employer, which means some decisions become joint decisions and certain liabilities are shared.
A payroll company has none of that structure. You write the checks (figuratively); they process the math. Liability stays entirely with you. Benefits sourcing stays entirely with you. Compliance stays entirely with you.
What each actually does.
| Function | Payroll Company | PEO |
|---|---|---|
| Payroll processing | Yes | Yes |
| Tax filing | Yes (under your EIN) | Yes (under PEO's EIN) |
| Health benefits sourcing | No (you source independently) | Yes — bundled or open-market |
| Workers' compensation | No (you source independently) | Yes — under PEO's master policy |
| 401(k) administration | Often add-on, separate | Bundled, often via MEP |
| HR compliance support | Limited or none | Included, varies by provider |
| Employment liability | Stays with you | Shared (co-employer model) |
| State unemployment (SUI) | You manage | PEO manages under their account |
| Onboarding workflows | Basic | Integrated I-9, W-4, benefits |
| Cost (typical SMB) | $30–80 per employee / month | $120–250 per employee / month |
The cost difference is real but misleading on its own. A payroll company at $50 PEPM that leaves you to source health insurance, manage workers' comp, and handle compliance separately may cost your business more in total than a $180 PEPM PEO that bundles those functions and brings group leverage on benefits pricing.
When a payroll company is the right answer.
- You're under 10 employees and the PEO admin overhead doesn't pay for itself yet
- You have strong existing benefits through a parent company, professional association, or industry group
- You don't want a co-employer for legal, contractual, or operational reasons
- You have internal HR capacity and don't need outsourced compliance or HR consulting
- Your industry has unusual benefits norms that don't fit standard PEO offerings
When a PEO is the right answer.
- You're between 10 and 250 employees — the size range where PEO economics work best
- Benefits cost is a recruiting constraint — group leverage produces materially better plans
- You don't have a dedicated HR function and don't want to build one
- You're in a multi-state or compliance-heavy business — SCA, prevailing wage, multi-jurisdictional payroll
- Workers' comp is a meaningful line item — trades, construction, hospitality, healthcare
- You're growing fast and need infrastructure that scales without building internal HR
The decision framework, honestly.
The "should I get a PEO" question has a structural answer most buyers don't run. The math:
- What does my current benefits stack actually cost? All-in: health, dental, vision, life, disability, 401(k) admin. Most buyers underestimate this by 20–40% because the costs are scattered.
- What's my workers' comp running, and could it be structured differently? Class-code analysis is genuinely the highest-leverage diagnostic in this whole framework.
- What's my real HR overhead? Time spent by founders, managers, or your one HR person on compliance, benefits administration, and employee questions. Convert to dollars.
- What's my exposure on the compliance lines I'm not actively managing? ACA filings, multi-state withholding, FLSA classifications, wage-and-hour. The cost of getting this wrong is rarely modeled.
Once those four numbers are real, the PEO-vs-payroll question becomes a math problem instead of a marketing exercise. The PEO usually wins between 15 and 200 employees. Outside that range it depends.
The question isn't "PEO or payroll company." The question is what you're actually trying to outsource.
What changes structurally when you move to a PEO.
- Your employees get the PEO's federal EIN on their W-2s. This sometimes raises questions during mortgage or background-check processes — usually resolved with a letter from the PEO.
- Your benefits open enrollment runs through the PEO. Plan options come from the PEO's offerings (or open-market sourcing, depending on the PEO).
- Your workers' comp policy moves under the PEO's master policy. You may want to confirm with your liability insurer; some commercial general liability policies reference WC structure.
- Your unemployment claims experience moves under the PEO's account. This can be a positive or a negative depending on your prior experience and the PEO's account history in your state.
- Your 401(k) typically moves into the PEO's plan — often a Multiple Employer Plan with institutional pricing. The transition has rules (Form 5500, vesting, plan documents) that should be handled by the PEO's retirement team.
None of these are problems. They're transitions. A PEO that walks you through them cleanly during onboarding is doing the work. A PEO that surprises you with them at month four is the wrong PEO.