Absence Rates Project Time Calculator
Estimate how employee absence rates can affect available team capacity and the time needed to complete a project.
Overview
This Absence Rates Project Time Calculator estimates how staff absences affect team capacity and project duration. Enter the total work required, team size, weekly working hours, and an expected absence rate to see an absence-adjusted timeline.
How it works
The calculator starts with the team's scheduled weekly hours by multiplying team size by weekly hours per person. It then deducts the selected absence percentage to estimate productive capacity. Total project work is divided by this reduced weekly capacity to estimate the project duration. Any additional contingency percentage is added to that duration.
How to use this calculator
- 1Enter the total number of productive work hours required for the project.
- 2Add the number of people expected to work on the project.
- 3Enter each person's scheduled working hours per week.
- 4Set the average absence rate expected during the project.
- 5Add contingency time if you want an allowance for other unplanned delays.
- 6Review the estimated duration and productive weekly capacity.
Example Calculation
Total project work
800
Team size
5
Working hours per person each week
40
Average absence rate
8%
Additional contingency
0%
Estimated project duration
4.3478260869565215 weeks
A team scheduled for 200 hours per week loses an estimated 16 hours to absence, leaving 184 productive hours per week. An 800-hour project is estimated to take about 4.3 weeks rather than 4 weeks.
Frequently asked questions
What is an absence rate in project planning?
An absence rate is the percentage of scheduled working time expected to be unavailable because of sickness, leave, personal time, or other absences.
How does employee absence affect a project timeline?
Absence reduces the productive hours available each week. If the amount of project work stays the same, reduced capacity generally increases the time needed to finish it.
Should annual leave be included in the absence rate?
It can be included if it is likely to affect the project period. For a more detailed plan, scheduled leave and public holidays may be planned separately.
Does this calculator account for task dependencies?
No. It assumes work can be completed steadily using the available team capacity. Dependencies, approval delays, and specialist bottlenecks can make a project take longer.
What contingency rate should I use?
Choose a contingency that reflects the uncertainty in your plan. Higher uncertainty, changing requirements, or tightly linked tasks may justify a larger allowance.
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Assumptions and warnings
Assumptions
- The absence rate is treated as an average percentage of scheduled working time across the whole team.
- All available team members are assumed to have the skills and access needed to complete the project work.
- Project work is assumed to be evenly distributed over the planned period.
- The result is a planning estimate and does not account for task dependencies, holidays, onboarding, or changing workloads.