Impact Tech Solutions · HSE Calculators
SEVERITY RATE

Severity Rate Calculator

Where TRIR and LTIFR measure how often injuries happen, Severity Rate measures how bad they are — using total lost workdays rather than case counts.
Severity Rate (per Hours Worked)
Average Days Lost per Case
The standard, most widely-used definition — normalizes lost workdays against exposure hours, comparable across organizations of any size. This is the version used in ISO 45001, IOGP, and most client pre-qualification reporting.
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SEVERITY RATE
A simpler, secondary measure — the plain average number of days lost per recordable case. Not normalized by exposure hours, so it can't tell you whether your workforce is getting safer as headcount changes, but it's a quick, intuitive read on "how bad is a typical injury here."
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AVERAGE DAYS LOST PER CASE

Formula Reference

Severity Rate = (Total Lost Workdays × Base) ÷ Total Hours Worked — standard, hours-normalized version
Average Days Lost per Case = Total Lost Workdays ÷ Number of Recordable Cases — simpler, non-normalized version

What Counts as a "Lost Workday"?

Per OSHA convention: any calendar day (following the day of injury) that the employee could not work at all due to a recordable injury or illness. The day of injury itself is excluded. Restricted/light-duty days are tracked separately on the OSHA 300 log (Column I) and may or may not be included depending on your organization's policy — document your convention and apply it consistently.

Severity Rate vs. TRIR/LTIFR

A company can have a low TRIR but high Severity Rate if its few incidents are serious (e.g., fractures, amputations) — or a high TRIR but low Severity Rate if incidents are frequent but minor. Track both together for a complete picture: frequency tells you how often something goes wrong; severity tells you how bad it is when it does.
Based on standard OSHA-aligned severity rate methodology (using the same 200,000-hour constant as TRIR/DART) and the ILO/international 1,000,000-hour convention. Lost workday counts should follow OSHA 29 CFR 1904 definitions (Column K of the OSHA 300 log) or your applicable local recordkeeping standard. There is no universal "good" severity rate — benchmark against your specific industry's published data rather than a generic threshold. For customized calculators tailored to your organization, please contact Impact Tech Solutions.