Abnormal turnover is the part of employee departures that exceeds an expected level. Analysts might estimate expected turnover using similar employers, industry patterns, company history or changes in the labor market. Actual turnover minus that benchmark gives an excess departure measure.
This can be more informative than comparing raw resignation rates. A technology company may face high turnover because the whole sector is hiring aggressively, while a retailer may experience normal seasonal variation. A benchmark attempts to distinguish company-specific changes from those broader forces.
The measure is only as credible as the comparison. Voluntary departures, layoffs and retirements should not be mixed without explanation, and headcount changes alter the rate's denominator. A sharp office-policy change occurring alongside layoffs or reduced compensation can also complicate causal attribution.
When reading research about RTO mandates, ask how normal turnover was predicted, whether senior and junior employees were analyzed separately and how uncertainty was reported. Abnormal turnover is a comparison statistic, not direct proof of the reason anyone left.