Staffing calculator: cases and processing time
Staffing follows from the working time all cases of a period need, divided by the working time of one full-time equivalent in the same period. With the number of people available the calculator also shows utilization and backlog. The accounts payable team from the worked example is filled in.
How the calculator works
The formula
Demand and capacity are calculated in hours per period. With 220 working days a year, a month has 220 ÷ 12 = 18.33 working days and a week 220 ÷ 52 = 4.23.
The example filled in
1,000 invoices a month at 16 minutes each need 266.7 hours. Two people who spend 90% of their time on this process bring 2 × 0.9 × 8 × 18.33 = 264 hours. Utilization is 101%: 266.67 − 264 = 2.67 hours are missing every month, and 2.67 ÷ 266.67 × 1,000 = 10 invoices are left over. On paper 1.82 FTE would be enough – but only if that time is really free for the process.
Estimate availability honestly
Hardly anyone spends eight hours a day on a single process. Meetings, other tasks and sickness belong in the availability. Holidays and public holidays do not: they are already taken out of the working days per year (default 220). Deducting them from the availability as well counts them twice.
Example: accounts payable loses 5% of its time to meetings and about 5% to sickness, so availability is 90% and capacity 264 hours a month. Deducting the 30 days of annual leave again (30 ÷ 220 = 13.6%) would leave 76.4% and 224 hours, and utilization would rise from 101% to 119%. Estimating too optimistically, on the other hand, calculates away a bottleneck that is real. More in the lesson Staffing and utilization.
Same calculation as the editor
The calculator builds a process with one role and one step and calculates it with the same function as the editor. In the editor you spread the work across several roles and see which one has the highest utilization; from 85% it is the bottleneck. Total staff demand there counts only your own staff, that is roles and departments, not external partners, customers or IT systems.
Frequently asked questions
Why is 100% utilization too much?
Cases do not arrive evenly. At full utilization there is no buffer for peaks, and every fluctuation lengthens waiting times. The app therefore marks roles amber from 85% and red above 100%; the role with the highest utilization from 85% is the bottleneck and is marked red as well.
Where do I get the processing time per case?
From mapping the current process: estimate each step and add them up across the process, weighted by visits; all parallel branches count. That is the processing time per case. In the editor this happens automatically for each role.
Does waiting time count towards staffing?
No. Demand comes only from processing. Waiting time extends the lead time but does not tie up working time.