Picking a PEO When You Bill by the Hour

A services firm's payroll isn't overhead the way it is at a product company. It's closer to cost of goods sold, since every consultant, engineer, or analyst on staff is inventory you're renting out by the hour. Payroll runs unusually high as a share of revenue in this sector¹, which means a PEO's fee structure moves your margin more here than it would at a retailer or a manufacturer.

That's the lens to run both vendors through. Justworks publishes a flat monthly rate per employee, so you can model the fully loaded cost of your next hire before you make an offer. TriNet quotes a custom package, often priced as a percentage of payroll or a negotiated per-head fee, which can move in either direction depending on your staff's compensation mix and the benefits tier you select.

Enterprise clients routinely run vendor security and insurance reviews before signing anything larger than a small statement of work. They want proof of workers' compensation, general liability, and often employment practices liability insurance (EPLI) naming them or their program as covered.

TriNet issues certificates of insurance through a dedicated compliance team and assigns a human HR contact who can answer a client's questionnaire about background checks or termination policies without looping in your own staff. Justworks automates certificate issuance for standard requests and handles most questionnaires through its support team rather than a named account contact. If your pipeline includes enterprise or government-adjacent clients who run formal vendor audits, weigh how much hand-holding those reviews actually need before assuming the cheaper option saves you time.

Almost no services firm delivers exclusively through W-2 staff. Fractional specialists, surge contractors, and subcontracted subject-matter experts fill the gaps between projects, and none of them touch your PEO relationship at all, since a PEO co-employs your payroll staff, not your independent contractors.

What differs between the two vendors is how much friction sits around managing that mixed roster. Justworks offers contractor payment and 1099-NEC filing tools, so check which plan includes them and whether any fees apply. TriNet offers contractor management tools too, but treats them as a separate workflow with its own onboarding, which fits firms that already have someone dedicated to vendor compliance more than it fits a ten-person shop running lean.

State unemployment insurance wage bases reset when your legal employer of record changes mid-year, because the PEO's master account becomes the employer for tax purposes. Firms that move onto a PEO in July instead of January can end up paying unemployment tax twice on the same wages within one calendar year.

Both vendors run onboarding teams that will walk you through this timing, but neither one waives the tax exposure for you. If your firm is mid-fiscal-year, ask each vendor for a written estimate of the SUTA reset cost before you sign anything, not after.

Run these before you take a demo from either vendor:

• Pull your trailing twelve months of payroll and divide it by revenue. If that number is well above what you'd expect for your sector, a flat per-employee fee will move the needle more than a percentage-of-payroll model.
• List every enterprise or public-sector client in your pipeline and note whether any of them run formal vendor security reviews.
• Count how many people on staff are billing hourly against a project code versus salaried overhead, since that split affects how much a PEO's time-tracking integration actually matters to you.
• Check your fiscal year start date against your target PEO switch date.

A firm can usually answer all four in the time it takes to read this section, and the answers point toward one vendor more clearly than a features comparison ever will.