The first cost
The probation review arrives and the file is thin, so the decision is rebuilt from recollection. Colleagues quietly absorb work. Training or coaching is prescribed before anyone has separated a skill gap from a response, workload or environment problem. The first cost is management attention; replacement, if it comes, is the final invoice.
The arithmetic
At 17% of a 1,880-hour working year, the management burden is approximately 320 hours—eight forty-hour working weeks. If the person eventually leaves, Gallup estimates that replacement may cost between one-half and two times annual salary. Actual cost varies by role, market and method of calculation.
Source
Robert Half (2012): U.S. CFOs surveyed estimated that supervisors spent an average of 17% of their time overseeing poorly performing employees. This was an executive estimate rather than a time study, and it is historical. ≈320 hours is an AERTHEIX illustration using 1,880 annual working hours. Gallup (2019) described one-half to two times annual salary as a conservative replacement-cost range.