Productivity, Utilization Rate & Interruption Cost

Billable utilization rate and cost of interruptions: the maths

Billable utilization is billed hours divided by hours worked: 26 h out of 37.5 h gives 69.3%. The tool also estimates the time lost refocusing (interruptions per day × recovery minutes) and prices it at the loaded hourly cost, using gross salary multiplied by 1.42.

Formulas

• Utilization = billable hours ÷ total weekly hours × 100.
• Time lost per day = interruptions × refocus minutes ÷ 60, capped at 6 h; then × 5 days and × 44 working weeks a year.
• Loaded hourly cost = annual gross salary × 1.42 ÷ (44 × weekly hours).
• Deep Work = daily hours − time lost − (admin hours + training and BizDev hours) ÷ 5, as a share of the day.

Example with the default values

37.5 hours worked, 26 of them billable: 69.3% utilization, classed as below target. With 14 interruptions a day and 15 minutes to refocus, 210 minutes are lost, i.e. 3.5 h a day, 17.5 h a week and 770 h a year. For a €52,000 gross salary the loaded cost is €44.75 an hour, so €34,459 lost per person per year and €172,293 for a team of 5. With 5 hours of training and BizDev a week, focused work left is 1.7 h a day (7.5 − 3.5 − 1.3 − 1), or 23%.

Assumptions and limits

• Categories: below 60%, admin overload; 60 to 75%, below target; 75 to 85%, optimal; above 85%, burnout risk. These are consulting rules of thumb, not a standard.
• The 1.42 factor stands for average French employer contributions; it is an indicative, unverified value that varies widely with salary and relief schemes.
• Every refocus minute counts as lost, even if it overlaps meetings or admin time.

Treat the output as an order of magnitude for discussing organisation, not as a measurement of working time.

Sources and dates: the average of 23 minutes and 15 seconds to get back to an interrupted task comes from Gloria Mark's research at the University of California, Irvine, as reported in a Fast Company interview; the tool defaults to 15 minutes (checked 14/10/2026).

Frequently Asked Questions

How do you calculate a billable utilization rate?

Divide the hours billed to clients by the hours worked in the week, then multiply by 100. With 26 billable hours out of 37.5, the rate is 69.3%. Admin, internal meetings and training make up the rest.

What utilization rate should a consultancy or agency aim for?

The tool uses a common benchmark of 75 to 85% billable hours; it flags admin overload below 60% and burnout risk above 85%. Between 60 and 75% it shows below target. These thresholds are industry habits, not a rule.

How long does it take to refocus after an interruption?

Research by Gloria Mark at the University of California, Irvine, found an average of 23 minutes and 15 seconds to get back to an interrupted task. The tool defaults to 15 minutes, which you can change. With 14 interruptions of 15 minutes, 3.5 hours a day are lost.

How does the tool put a price on a lost hour?

It multiplies annual gross salary by 1.42 to approximate the employer cost, then divides by 44 working weeks and by weekly hours. For €52,000 gross and 37.5 hours that gives €44.75 an hour. The factor is an indicative average, not a legal value.

Is this tool really free?

Yes, all tools on Kristools are 100% free and accessible without registration.

Is my data protected?

Yes. All processing is performed directly and securely inside your browser. No personal data is sent to our servers.