Absence Rates Project Time (Team) Calculator FAQ
Answers to common questions about estimating project time, team capacity, and schedule extensions when staff absences are expected.
This FAQ explains the inputs, outputs, assumptions, and practical interpretation of an absence-adjusted project time estimate. Results are intended for general planning and should be considered alongside project-specific risks.
General project absence questions
Basic terms used when estimating the schedule effect of staff absence.
What does the Absence Rates Project Time (Team) Calculator estimate?
It estimates the working-day and working-week duration of a fixed project workload after reducing average team capacity for an expected absence rate.
What counts as an absence rate?
It is the percentage of planned working time expected to be unavailable due to sickness, leave, caring responsibilities, training, or other absences included in the planning assumption.
What is a person-day?
A person-day is the amount of project effort one person can deliver in one normal working day. It measures effort, not calendar time.
Is the result a calendar completion date?
No. The calculator produces working-time estimates. Calendar dates also require allowance for weekends, public holidays, closures, dependencies, and other schedule constraints.
Inputs and calculation method
How the calculator turns workload, team size, and absence assumptions into a duration.
How is planned working duration calculated?
The baseline duration is project workload divided by team size. It assumes the full assigned team is available for all planned work.
How does the calculator reduce team capacity?
It multiplies team size by one minus the absence rate. For example, 10 people at 5% absence give average effective capacity of 9.5 people.
Why does the project workload stay the same in the calculation?
The model assumes the amount of work required is unchanged. Absence affects the available capacity available to complete that work.
What should I enter for team size?
Enter the average full-time-equivalent capacity assigned to the project, rather than including people who are not expected to work on it.
What does working days per week change?
It converts the adjusted working-day result into working weeks. It does not change the underlying workload or effective team capacity.
Interpreting results
What the calculator outputs mean in a schedule planning context.
What is effective team size?
Effective team size is the average number of full-time-equivalent people expected to be available after the absence rate is applied.
What is the schedule extension?
It is the estimated number of extra working days compared with a plan based on full attendance.
What are expected lost person-days?
They are the estimated additional capacity time that must be allowed for to complete the original workload at the stated absence rate.
Why can the calculated extension be a decimal number?
The model uses average capacity across the project. A decimal result is normal and can be rounded for practical scheduling where appropriate.
Can I compare several absence assumptions?
Yes. Running low, expected, and higher absence scenarios can show how sensitive the schedule is to different availability assumptions.
Accuracy and planning limits
Factors that can cause actual delivery time to differ from the estimate.
Does the calculator account for specialist roles?
No. It treats capacity as broadly interchangeable. Absence from a critical specialist may cause a larger delay than the average-capacity estimate indicates.
Does it include public holidays and weekends?
No. It calculates project working time only. Add non-working dates separately when preparing a calendar schedule.
Does it include scope changes or rework?
No. The calculation assumes the workload is unchanged and does not model additional work or changes in project scope.
Can actual delivery be faster than the estimate?
Yes. Actual absence may be lower than assumed, or the team may complete work more efficiently than the original workload estimate suggests.
Should this result replace a detailed project plan?
No. It is a high-level capacity estimate and does not replace task sequencing, resource scheduling, risk management, or project controls.
How does absence affect project duration?
When average team availability falls, the same workload takes longer. The calculator divides the workload by the reduced effective team capacity.
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