The biggest PEO companies

Advertised prices, verified

How to compare the biggest PEOs

1. Start from certification, not size. The IRS certifies professional employer organizations that meet federal requirements for financial responsibility, tax compliance and US presence, and publishes a public list of certified PEOs. Shortlist from that list first; scale without certification is not a substitute.
2. Get per-employee pricing in writing. Large PEOs quote either a flat fee per employee per month or a percentage of payroll. Ask for the same structure from every vendor you compare, itemised against your actual headcount and salary levels, so the quotes are comparable.
3. Compare the health plan, not the brochure. Ask which carrier underwrites the plan, how renewals have moved over the last three years, and what happens to your rates if your group's claims run high. The plan is most of the value of a big PEO, so it deserves most of the diligence.
4. Check the exit before you sign the entry. Ask what notice the contract requires, whether your employees can stay on comparable coverage if you leave, and how employment tax filings are handled in a mid-year transition. The biggest providers publish standard terms; read them before onboarding.

Who the biggest PEOs are

ADP TotalSource describes itself as the largest certified professional employer organization in the United States, and reported passing half a million co-employed worksite employees in early 2018 in its own press materials. It is a certified PEO, which under the IRS programme required meeting specific bonding and independent financial-review requirements.

TriNet, founded in 1988 in the San Francisco Bay Area and listed on the NYSE under TNET, reported roughly 323,000 worksite employees as of the end of 2025 on its own site, and sells both a PEO and an administrative services product aimed at small and medium businesses. Insperity and Paychex round out the group usually named among the largest US PEOs; both are publicly traded and sell PEO services alongside broader payroll and HR products. These figures are the companies' own statements, reported here without endorsement.

Does biggest mean best value

Scale buys plan depth and administrative maturity, but it does not automatically buy the lowest fee. The largest PEOs tend to price at a premium for their benefits pool, and some are selective about which industries and states they onboard. A smaller or regional PEO can beat them on fee and attention for a company whose workforce is concentrated in one state, or whose industry the large providers rate as higher risk.

The comparison that matters is total cost against what you get: the administration fee, the workers' compensation rate, the health plan employee-level premiums, and the terms for leaving. This site's index verifies advertised pricing against each vendor's own pages where it is published; where a vendor quotes only by sales call, the table says so rather than guessing. Nothing here is legal or tax advice, and the vendor's contract controls what is actually delivered.

Common questions

Which PEO is the largest in the US?

ADP TotalSource calls itself the largest certified PEO in the United States in its own press materials, and passed half a million worksite employees in 2018. TriNet reported roughly 323,000 worksite employees at the end of 2025. Exact rankings move with each company's reporting period.

Are the biggest PEOs IRS-certified?

The IRS runs a voluntary certification programme and publishes a public list of certified PEOs. Several of the largest providers hold certification; verify any specific vendor against the IRS public listing rather than the vendor's marketing.

Do big PEOs cost more than small ones?

Often, per employee, because their benefits pools and service layers price at a premium. Whether that premium pays for itself depends on how much your team values the health plan; for a workforce that declines coverage, a leaner provider is usually cheaper.

Is a PEO the same as an EOR?

No. A PEO co-employs staff you already employ through your own US entity. An employer of record is the sole legal employer where you have no entity, which is the usual tool for hiring abroad. Several vendors sell both, at different prices.

Coverage by country

• Employer of record vendors covering Singapore
• Employer of record vendors covering Mexico
• Employer of record vendors covering Spain
• Employer of record vendors covering Colombia
• Employer of record vendors covering United Kingdom
• Employer of record vendors covering France
• Employer of record vendors covering Hungary
• Employer of record vendors covering New Zealand