Lost Workday Rate

Last updated: May 13, 2019

What Does Lost Workday Rate Mean?

The Lost Workday Rate (LWR) is a standardized metric that provides a measure of the total number of working days lost within a workplace due to occupational injury or illness. The formula for calculating LWR is prescribed by OSHA to ensure that all workplaces calculate the statistics the same way, thus guaranteeing the accuracy of the data. The LWR formula is defined as the total number of workdays lost multiplied by 200,000, divided by the total number of hours worked by all employees within a given period.

[Number of workdays lost] * 200,000 / total number of hours worked

The number 200,000 is used to represent 100 employees working 2,000 hours per year, as the rate that results from this formula is designed to represent the number of lost workdays per 100 employees. Every workplace’s LWR is given as workdays lost per 100 employees, regardless of the actual number.

Safeopedia Explains Lost Workday Rate

The LWR is a lagging indicator of a company’s safety performance. When used as a complement to OSHA’s recordable injury and illness requirements, it provides information about the severity and impact of the illnesses and injuries that occur within a given work context. As a lagging indicator, it only describes a workplace’s past safety performance and therefore does not function as an accurate predictor of future safety performance.

OSHA provides workplaces with a number of different safety incident formulas that can be used to understand safety performance. Because rates are calculated in terms of “rate per 100 employees,” the LWR is primarily used by larger companies. A single additional lost day within a workplace with a small number of employees could produce a large fluctuation in LWR, limiting its usefulness within smaller work settings.

As with every other OSHA incidence rate, the LWR is based on the number of injuries and illnesses recorded within an employer’s OSHA 300 log. This log is a record of all significant injuries that occur within a workplace in a given year. Employers maintaining workplaces with 10 or more employees are required by law to maintain an OSHA 300 log.

All of OSHA’s incidence rate formulas are standardized to 100-employee workplaces. For instance, the DART rate (“days away, restricted, or transferred”), which includes both the number of days lost, as well as the number of days an employee is present at work but cannot perform regular duties, is also calculated per 100 employees. This standardization allows workplace safety performance to be compared between workplaces that exist within the same industry and that have a similar number of employees.


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