INCIDENT RATES · US OSHA METHOD
How to calculate TRIR
You need two matching records: total recordable cases and employee hours worked. The arithmetic is simple; choosing consistent inputs matters just as much.
By HSECalc · Published and references checked
1. Choose a consistent scope
Write down the site or workforce and reporting period before entering anything. Cases from one site and hours from a wider business do not describe the same population.
- Cases: use total OSHA-recordable cases for that scope, including work-related fatalities. A near miss is not automatically a recordable case. This guide does not decide recordability: consult OSHA 1904.7 and the applicable recordkeeping rules.
- Hours: use actual employee hours worked, including overtime. Exclude paid leave that was not worked. If actual records are unavailable, use the estimation instructions supplied with OSHA Form 300A and record that the figure is estimated.
A man-hours calculation can help check arithmetic for a shared schedule, but a planned schedule is not automatically a record of actual hours.
2. Apply the formula
The fixed base represents 100 people working 40 hours per week for 50 weeks. It standardises the rate; it is not an instruction to enter 200,000 as your actual hours. See OSHA's formula explanation.
A fictional worked example
Suppose the same workforce records 3 recordable cases and 250,000 hours worked during the chosen period.
- Multiply cases by the base: 3 × 200,000 = 600,000.
- Divide by actual hours: 600,000 ÷ 250,000 = 2.40.
Report: “TRIR 2.40, based on 3 recordable cases and 250,000 hours worked,” with the workforce and period identified. Do not attach a percentage sign.
Try the same figures in the calculator ↗3. Interpret the rate with context
A rate of 2.40 expresses the entered case experience on the 200,000-hour basis. It does not mean 2.4% of employees were injured, and it does not count how many days were lost.
There is no universal TRIR number that certifies a workplace as safe. Comparisons need a compatible industry, establishment size, period and case definition. One case can move a small workforce's rate sharply. OSHA advises using more than one performance measure; read its interpretation on small establishments and indicator limitations.
Investigate the events and check whether corrective actions actually control the hazard. Consider exposure information, reporting quality and prevention work alongside historical case rates. A low number should never be a reason to discourage reporting.
Common input mistakes
- Entering headcount as hours. A team of 100 people does not mean 100 hours.
- Counting lost days instead of cases. One case with several days away is still one case in this numerator.
- Changing the base for a shorter period. Keep 200,000 and label the reporting period clearly.
- Mixing methods. DART uses a narrower case group; LTIFR uses a different case definition and stated hours basis. Their values are not interchangeable.
Common questions
What if there are zero cases?
With positive hours, zero cases gives a rate of zero. It describes those records; it does not demonstrate that every hazard is controlled. Zero hours cannot be used as a denominator.
Can I average monthly TRIR values?
To combine periods, add their case counts and their hours, then apply the formula once. A simple average of rates can mislead when monthly hours differ.
Can this replace UK accident reporting?
No. This guide explains a US-method performance calculation. Using it internationally does not establish compliance with local recording or reporting duties.
Original references
- OSHA: clarification of incidence-rate calculation — formula, fixed base and interpretation.
- OSHA forms and instructions — choosing case and employee-hour inputs.
- OSHA 1904.7 — general recording criteria.
- BLS occupational safety and health field definitions — incidence-rate basis.
HSECalc is independent and is not endorsed by OSHA or BLS. Report an error or unclear explanation.