Build the full-time number first (from Notes 1 & 2). Canadian salary sources for an HR Manager in Ontario vary widely by methodology: Indeed reports an Ontario average of $85,644 (604 salaries, updated May 2026); ZipRecruiter ~$76,515 for HR Manager and $103,234 for Senior HR Manager; PayScale ~C$73,000; while survey-based sources skew higher (Salary.com median ~C$136,000 for Toronto, ERI ~$146,000). Government of Canada Job Bank (NOC 10011, Manager-Human Resources) shows an hourly range of roughly $37.94–$87.18. A reasonable planning base for a senior HR Manager/Director in the K-W area is ~$95,000–$130,000. Apply the ~1.25–1.4× loaded multiplier (Note 2) and add one-time cost-to-hire (SHRM’s benchmark cost-per-hire is ~$4,700, and far more for senior roles — SHRM’s 2025 data puts executive hires near 7× non-executive). All-in first-year cost for a full-time senior HR hire therefore lands roughly in the $130,000–$185,000 range, recurring at ~$120k–$170k thereafter — plus recruiting risk (see Note 3: senior mis-hires are power-law expensive).

The fractional number (market-variable, label vendor). Fractional/on-call HR is priced as a monthly retainer or day-rate. Canadian market data (vendor-sourced, so directional) shows tiered retainers such as ~$2,995/month for advisory-level support (~5 hrs/week), ~$6,995/month for HR management (~10 hrs/week including execution), and ~$9,995/month for fractional HR-Director-level strategic leadership (~15 hrs/week). General Canadian ranges run $2,500–$10,000+/month, with hourly rates of roughly C$100–225 depending on seniority. At, say, $5,000/month, a fractional engagement is ~$60,000/year — materially below the all-in cost of a full-time senior hire while still delivering senior-level expertise.

The structural conclusion (honest, no fabricated %). The decision is driven by utilization, not a fixed savings percentage:

Fractional is cost-favourable when the genuine HR workload is below roughly half-time, when the need is episodic (policy build-out, an investigation, a restructuring, compliance catch-up), or when an SMB needs senior judgment it cannot justify employing full-time. A 20–60 person K-W employer typically falls here.
Full-time wins at sustained high volume — once HR work reliably exceeds ~0.6–0.8 FTE (continuous recruiting, large/complex workforce, daily employee-relations load), the fixed monthly retainer stops being cheaper than salary, and an in-house hire also adds availability and embeddedness. This is typically the 100–200-person band.
A common hybrid for the 60–100 band: a fractional senior leader plus a junior in-house coordinator.

We deliberately do not publish a single “fractional saves X%” figure — savings depend entirely on hours used versus a full-time salary, and quoting a precise percentage would be false precision. The structural logic is industry-consensus; the specific dollar figures and fractional rates are directional (salary sources disagree; fractional pricing is market-variable).

Anchor: Fractional / On-call HR pillar. Built from Note 1 (cost-to-hire), Note 2 (loaded cost); links to Note 4 (vacancy cost of going without HR).