Use the severity rate calculator to measure the number of workdays lost to workplace injuries and illnesses relative to the total hours worked during the same period.
Enter your total lost workdays and total hours worked below. You can calculate the severity rate using a base of either 200,000 hours or 1,000,000 hours.
Severity Rate = (Total Lost Workdays × Reporting Base) ÷ Total Hours Worked
A severity rate adds context that an incident count cannot provide. Two sites may each record three lost-time incidents during a year, but one may lose 12 workdays while the other loses 120. Their incident counts are identical, but the amount of lost time is very different.
Tracking severity rate alongside measures such as TRIR, DART and LTIFR helps safety teams distinguish between how often incidents occur and how much lost time those incidents cause.
Severity rate is calculated from the number of workdays lost, the total employee hours worked during the same period and the reporting base being used.
For a rate based on 200,000 hours:
Severity Rate = (Total Lost Workdays × 200,000) ÷ Total Hours Worked
The 200,000-hour figure represents the annual hours of 100 full-time employees working 40 hours per week for 50 weeks. Using a common base allows organizations with different workforce sizes to express their results on the same basis.
Consider a manufacturing facility with:
Using a 200,000-hour base:
Severity Rate = (30 × 200,000) ÷ 400,000
Severity Rate = 15
The facility recorded 15 lost workdays per 200,000 hours worked.
The same calculation can be performed for a site, project, department, business unit or an entire organization. The lost-workday figure and employee-hours figure must cover the same workforce and reporting period.
The definition used for lost days needs to be consistent. Otherwise, comparisons between reporting periods or locations can be misleading.
For OSHA recordkeeping, days away from work are counted as calendar days, rather than only the employee's scheduled working days. This can include weekends and holidays if the employee would have been unable to work because of the occupational injury or illness.
The day the injury or illness occurs is not counted as a day away from work. Counting starts on the following day.
OSHA also distinguishes between:
These figures should not automatically be treated as interchangeable when calculating severity rate.
If your organization calculates severity rate using only days away from work, continue using that definition when comparing results. If your company, client or industry reporting framework includes restricted or transferred days, state this in the methodology.
OSHA recordkeeping also places a 180-calendar-day cap per case on the combined number of days away from work and days of job transfer or restriction entered on the OSHA 300 Log.
Severity rate calculators commonly use one of two exposure bases.
Severity Rate = (Lost Workdays × 200,000) ÷ Total Hours Worked
The 200,000-hour base corresponds to 100 full-time employees working 2,000 hours each during a year. It is also the exposure base OSHA uses for rates such as TRIR and DART.
Severity Rate = (Lost Workdays × 1,000,000) ÷ Total Hours Worked
A one-million-hour base is also used by organizations that report occupational safety performance per million hours worked.
The choice of base changes the number reported, but it does not change the underlying safety performance.
For example, suppose a company records 20 lost workdays across 500,000 hours worked.
Using 200,000 hours: (20 × 200,000) ÷ 500,000 = 8
Using 1,000,000 hours: (20 × 1,000,000) ÷ 500,000 = 40
The results describe the same lost-time experience on different exposure bases.
Always check the reporting base before comparing severity rates. A rate of 40 per million hours is equivalent to a rate of 8 per 200,000 hours.
A severity rate shows how much lost time workplace injuries and illnesses have caused relative to the hours worked.
A lower rate means fewer workdays were lost for the same amount of employee exposure. A higher rate means more days were lost.
The number becomes more useful when compared with relevant historical or operational data.
For example, you can compare:
Avoid treating severity rate as a standalone safety score.
One serious injury can cause the rate to rise sharply, particularly in a smaller workforce. Conversely, a low severity rate does not show whether the workplace has uncontrolled hazards, recurring near misses or less severe incidents.
The incidents behind the number still need to be reviewed.
There is no single severity rate that can be considered good for every organization or industry.
Generic thresholds such as "below 10 is good" or "above 50 is poor" ignore differences in industry, workforce size, exposure, reporting practices and the reporting base used.
Looking at the trend can be more useful.
Consider this example:
| Year | Hours Worked | Lost Workdays | Severity Rate |
|---|---|---|---|
| 2024 | 500,000 | 60 | 24.0 |
| 2025 | 520,000 | 42 | 16.2 |
| 2026 | 510,000 | 55 | 21.6 |
Calculated per 200,000 hours worked.
The severity rate improved in 2025 before increasing in 2026.
The next step is to find out why.
The additional lost days may have come from several incidents. They may instead have resulted from one serious injury requiring an extended absence. Those situations present different risk profiles even though both affect the annual severity rate.
Severity rate is often reported alongside other safety performance indicators. They are related, but they do not measure the same thing.
| Metric | What it measures | Common calculation |
|---|---|---|
| Severity Rate (SR) | Lost workdays relative to hours worked | Lost workdays × reporting base ÷ hours worked |
| TRIR | OSHA-recordable cases relative to hours worked | Recordable cases × 200,000 ÷ hours worked |
| DART Rate | Cases involving days away, restricted work or job transfer | DART cases × 200,000 ÷ hours worked |
| LTIFR | Lost-time injuries relative to hours worked | Lost-time injuries × reporting base ÷ hours worked |
The important distinction is between cases and days.
TRIR, DART and LTIFR count qualifying cases or injuries. A lost-day severity calculation uses the number of days lost.
Suppose two sites each record two lost-time injuries during 1,000,000 hours worked.
At Site A, the two injuries result in a total of 10 lost days.
At Site B, the two injuries result in a total of 70 lost days.
Their lost-time injury frequency may be identical because each site recorded two injuries over the same number of hours. Their severity rates will be very different because the incidents at Site B resulted in considerably more lost time.
This is why frequency and severity are better reviewed together.
Lost days and hours worked must cover the same period.
If you are calculating severity rate from January through June, use both the lost days and hours worked for that six-month period.
A severity rate calculated per 1,000,000 hours will be five times the equivalent rate calculated per 200,000 hours.
Check the base before comparing results from different reports, sites or contractors.
The number of incidents and number of lost days are different inputs.
If four injuries resulted in a combined 48 lost days, a lost-day severity calculation uses 48, not four.
DART is based on the number of cases involving days away from work, restricted work or job transfer.
A lost-day severity calculation is based on the number of days lost.
For example, an incident that causes 30 days away from work represents one days-away case for a case-based rate, but contributes 30 days to a severity calculation based on lost days.
A high severity rate does not necessarily mean that a site is experiencing a large number of incidents.
One serious injury can account for a significant proportion of the lost days recorded during the year.
Review the cases contributing to the rate before drawing conclusions about why it has changed.
Report, manage and track safety incidents, observations and near-misses.
Request free trialStart with the cases responsible for the lost days.
If the rate has increased, identify which incidents contributed most to the change. Review the task being performed, type of injury, location, hazard involved, investigation findings and corrective actions.
Then look for recurring patterns.
Several manual-handling injuries resulting in lost time require a different response from one serious fall accounting for most of the year's lost days. The severity rate may increase in both situations, but the underlying causes are different.
For organizations with multiple locations, the same approach can be used to monitor severity rate by site, project, department or contractor.
Keep the calculation method consistent and review severity alongside incident frequency, investigation findings, corrective actions, near misses and other relevant safety indicators.
Severity rate is a lagging indicator. By the time it increases, the injuries and lost days have already occurred.
The practical use of the metric is to identify where lost time is coming from and use that information to improve risk controls.
Start with incidents responsible for the greatest number of lost days. Review whether:
A rising severity rate should therefore lead to investigation and action rather than simply another number on the monthly safety dashboard.
Calculating severity rate is useful, but the underlying incident data is what helps safety teams identify recurring hazards, investigate causes and follow corrective actions. Safetymint helps organizations manage workplace incidents, investigations and corrective actions in one system.
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