ASO vs PEO: Key Differences, Costs and How to Choose

When businesses start looking for HR support, two terms often come up: ASO and PEO. And if you're wondering what the difference is, you're not alone. While there are a variety of factors that make them different, the biggest difference comes down to co-employment. 

A PEO works through a co-employment relationship, while an ASO supports HR administration without becoming a co-employer. That structural difference shapes how benefits, payroll taxes, workers' compensation, and HR administration are supported. 

This guide explains how each model works, how costs are typically structured, and how to decide which level of service might be the best fit for your business. 

ASO vs. PEO Simplified

The easiest way to compare an ASO and a PEO is to look at the different functions each performs. 

Here's a side-by-side look at how ASOs and PEOs compare: 

Both models can help businesses manage HR more effectively. They just do it in different ways. An ASO keeps the business as the sole employer for payroll tax purposes and provides HR administration and expertise alongside your team members. A PEO and its client are in a co-employment relationship where certain employer-related responsibilities allocated between the client and the PEO under the client service agreement. 

What is an ASO? 

An ASO, or Administrative Services Organization, provides expertise and HR administration support such as payroll processing, payroll tax administration, benefits administration, HR best practice guidance, and compliance support. With an ASO, businesses retain control over their workforce, benefits strategy, and company culture while gaining access to HR expertise, payroll administration, compliance and employee support. 

Payroll taxes are filed under the company's EIN and the employer sponsors its own benefit plans, allowing it to maintain its existing provider relationships and decision-making authority. 

TriNet HR Plus is TriNet's ASO, designed for businesses that want access to comprehensive HR technology, administrative support, and access to dedicated HR expertise while being the employer of record for payroll tax purposes. 

What does an ASO help handle?

An ASO can help with many of your day-to-day HR functions, depending on the provider and services selected. Common areas of support include: 

Payroll processing and payroll tax administration: Support with payroll, payroll tax administration, and related workflows for payroll processed withing the ASO platform 

Benefits administration: Delivers benefits support and administrative support while enabling the business to maintain control of its benefits programs and strategy. 

HR best practice guidance and compliance support: Access to HR support, best practices, templates, and information that can help the business manage HR more confidently. 

HR technology: Tools that help automate and streamline HR tasks, employee data, payroll workflows, reporting, and benefits administration. 

An ASO can provide specialized expertise across HR, payroll, benefits administration, and compliance. Paired with comprehensive technology, this support helps streamline day-to-day operations, allowing businesses to managing their employees and benefits programs while benefiting from trusted best practices and administrative assistance. 

What is a PEO? 

A PEO, or Professional Employer Organization, provides small and medium-size businesses with a holistic HR solution through a co-employment relationship. The PEO often bundles the following services into a single solution: payroll services, access to benefits (health, retirement, voluntary), workers' compensation, compliance support, risk management support, HR best practice guidance, and HR technology. 

How does a PEO work? 

A PEO provides services through a co-employment relationship. In this arrangement, the business retains control of its employees, while the PEO takes on certain employer-related responsibilities as defined in the service agreement. 

For example, a PEO may process payroll based on client-provided information, report wages under the PEO's FEIN, remit and report payroll taxes for payroll processed in the PEO platform, provide access to large-group health and welfare benefits, help administer workers' compensation, and provide HR best practice guidance and compliance support. The exact responsibilities depend on the PEO and the terms of the service agreement. 

One common misconception is that a business loses control of its workforce when it works with a PEO. The businesses continue to direct and control the workforce, including  decisions about hiring, compensation, schedules, performance management, discipline, terminations, workplace culture, and day-to-day operations. 

Some PEOs may also be certified by the IRS or accredited by independent agencies such as the Employer Services Assurance Corporation. These designations can involve additional disclosures, certifications, requirements, or bonding obligations. 

ASO vs. PEO costs

ASO and PEO pricing can look different because the models include different levels of service and responsibility. 

ASOs typically price their services as an administrative fee based on the services selected, often on a per-employee per month (PEPM) basis. PEOs may charge an administrative fee priced per employee per month (PEPM) or as a percentage of payroll. Depending on the arrangement, charges for employee benefits, workers’ compensation, payroll taxes and optional services may be separate from the administrative fee. Because pricing and included services vary by provider and client circumstances, businesses should compare the full scope of services and total costs under each proposal. 

What about HRO? 

Human Resources Outsourcing, or HRO, is a broader term for outsourcing HR functions to a third-party provider. The functions typically covered include payroll, benefits administration, HR consulting, recruiting support, compliance support, or other administrative services. ASOs and PEOs are both types of HR outsourcing models. The difference is that an ASO supports HR administration while the business remains the sole employer, and a PEO provides a broader bundled service model through co-employment. 

How to choose between an ASO and a PEO

The right model depends on how your business wants to manage HR, benefits, employer-related responsibilities, and administrative complexity. Neither model is better outright. The better fit depends on your priorities. 

An ASO may be a good fit if your business wants to:

• Remain the employer of record for payroll tax purposes for  its workforce.
• Receive expert best practice guidance on payroll, benefits administration, HR documentation, and related tasks.
• Maintain more direct control over benefits strategy and vendor relationships.
• Access comprehensive HR and payroll technology.
• Either doesn't want to offer benefits or wants to sponsor its own business-provided benefits.

A PEO may be a good fit if your business wants to:

• Access a comprehensive HR bundle through one provider.
• Gain access to large-group benefits through the PEO relationship.
• Share or allocate certain employer responsibilities through a co-employment model.
• Get support with payroll tax administration, workers' compensation administration, HR best practice guidance, and risk management.
• Support growth across states with a more comprehensive HR infrastructure.

Businesses may be able to transition from a PEO to an ASO or vice versa as their needs change, although the transition may involve payroll tax reporting and other considerations. 

Find the HR model that fits your business 

Running HR can be a lot for a small or growing team to manage alone. But you don't have to figure it out by yourself. ASOs and PEOs both exist to help businesses get support, they just do it through different structures. 

TriNet supports both paths: TriNet HR Plus for businesses looking for an ASO model, and TriNet PEO for businesses looking for a co-employment model. Understanding the difference can help you choose the approach that best fits how your business wants to run HR.