How to Calculate True Utilization (and What Most PSAs Get Wrong)

Utilization is the most misunderstood simple metric at services firms.

The formula looks straightforward: billable hours divided by available hours. But “available hours” is where firms silently disagree with each other by 15 or more percentage points — and where most PSA tools default to the wrong answer.

This piece is a practitioner's guide to calculating utilization correctly, what the most common errors look like, and why the right denominator depends on the decision you're making.

The formula that looks simple

Utilization = Billable Hours ÷ Available Hours.

Billable hours is clean, if your time tracking is. See our piece on time tracking practices for why this is less obvious than it sounds.

Available hours is where the real debate starts. Three different answers all look reasonable; each produces a different number:

• Standard working hours (40/week): clean, but inflates utilization because it assumes everyone works exactly 40 hours.
• Actual worked hours: reflects reality but punishes people who work longer weeks by lowering their utilization percentage.
• Scheduled available hours: working hours minus PTO, holidays, approved non-billable time.

The third is the right answer for most decisions. The first is the wrong one, and it's also the default in many PSA tools.

Why the denominator matters

Consider a senior consultant: 40 standard hours, 6 hours of PTO that week, 32 billable hours logged, 8 additional hours on firm BD and internal work.

Three calculations:

• Standard denominator: 32 ÷ 40 = 80% utilization.
• Actual worked denominator: 32 ÷ 46 = 70% utilization (she actually worked 46 hours).
• Scheduled available: 32 ÷ 34 (40 - 6 PTO) = 94% utilization.

Same person, same week, three very different stories. The first says “healthy.” The second says “underperforming.” The third says “headed for burnout.”

None of them are wrong. They're answers to different questions.

The decision drives the calculation

The right denominator depends on what you're trying to decide:

For billing rate realization

Use actual worked hours. It answers: “Of every hour this person worked, how many got billed?” Critical for understanding margin leakage.

For staffing and capacity planning

Use scheduled available hours. It answers: “How much of this person's work time is going to client-billable work vs. firm non-billable?” Critical for deciding if someone has room for more.

For profitability analysis

Use fully-loaded cost hours. It answers: “After all benefits, overhead, and non-billable time, how profitable is this person's labor?” Critical for pricing and role mix decisions.

Firms that use one number for all three decisions make consistent mistakes. Firms that use the right number for each decision make better ones.

The PTO trap

Most common miscalculation: treating PTO as non-billable time in the numerator denominator, rather than removing it from the denominator entirely.

“Sarah was 75% utilized this week” — but Sarah took 3 days of PTO. She worked 16 hours total, all billable, out of 16 scheduled hours. Her utilization that week was 100%, not 75%.

Treating PTO as non-billable makes people look like they're underperforming every time they take a vacation, which drives bad decisions about headcount and burnout.

The fix is simple: PTO, holidays, and approved unplanned absence come out of the denominator. The person's utilization calculation uses the hours they were actually scheduled to work.

The rollup problem

Firm-level utilization is an average. Averages hide distributions, and distributions are where decisions hide.

See our utilization importance piece for why aggregate utilization is a trap: a firm at 74% blended could have half its people at 60% and half at 88%. The 74% tells you the firm is healthy; the distribution tells you half the firm is underworked and the other half is about to burn out.

Right calculation, right number, right distribution — all three matter.

Three rules for getting it right

1. Match the calculation to the decision. Don't use one number for everything. Billing, staffing, and profitability need different denominators.
2. Remove PTO and holidays from the denominator. Don't penalize people for taking time off.
3. Always look at distribution alongside aggregate. A healthy average with unhealthy distribution is still unhealthy.

Most PSA tools default to a single standard-hours calculation that hides more than it reveals. The firms that manage utilization well use the right number for each decision and look past the rolled-up average.

Octayne's Utilization module calculates billing, staffing, and profitability utilization separately, with PTO and holidays handled correctly by default. Book a demo to see all three views on your firm's data.