Calculate accident frequency rates from cases and employee hours, or estimate hours from staffing to report AFR, TRIR, LTIFR, or DART per work hours.
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Accident Frequency Rate Formula
The calculator uses a standard frequency rate formula. The base value changes the scale of the result but not the underlying ratio.
AFR = (Number of Accidents / Total Hours Worked) * Base
- AFR = Accident Frequency Rate (also used for TRIR, LTIFR, or DART)
- Number of Accidents = count of recordable cases in the period
- Total Hours Worked = sum of hours worked by all employees in the period
- Base = 1,000,000 hours (common AFR / LTIFR), 200,000 hours (OSHA TRIR / DART), or 100,000 hours
If you do not know the exact hours worked, the calculator estimates them from staffing:
Total Hours = Employees * Hours per Person * Period Length
- Employees = average headcount or full-time equivalents (FTE)
- Hours per Person = average hours per week (x52) or per year
- Period Length = years, months (/12), or weeks (/52)
Assumptions: hours include only paid time worked, not vacation or sick leave. One FTE defaults to 2,080 hours per year. Use the same case definition (all accidents, recordables only, lost-time only, or DART) consistently across periods you compare.
Calculator modes:
- Known hours applies the first formula directly. Enter cases and total hours, pick a base, and get the rate.
- Estimate hours runs the second formula first to build total hours, then feeds that into the first formula. Use this when payroll hours are not available.
- Metric selector (AFR, TRIR, LTIFR, DART) changes the result label only. The math is the same. Choose the base that matches the standard you report against.
Reference Tables
Use these as a sanity check on your result. Industry benchmarks shift year to year, so always compare against current published data for your sector.
| Metric | Cases Counted | Typical Base |
|---|---|---|
| AFR | All workplace accidents | 1,000,000 hours |
| TRIR | OSHA recordable injuries and illnesses | 200,000 hours |
| LTIFR | Injuries causing lost work time | 1,000,000 hours |
| DART | Days Away, Restricted, or Transfer | 200,000 hours |
| Industry (US, recent TRIR) | TRIR per 200,000 hrs |
|---|---|
| Construction | ~2.5 |
| Manufacturing | ~3.0 |
| Warehousing and storage | ~4.8 |
| Healthcare and social assistance | ~3.8 |
| Retail trade | ~3.0 |
| Professional and business services | ~0.9 |
Worked Examples and FAQ
Example 1 — Known hours. A site logged 6 accidents over 1,500,000 hours worked.
AFR = (6 / 1,500,000) * 1,000,000 = 4.00 per million hours.
Example 2 — Estimating hours. 750 employees, 40 hours per week, over 1 year.
Total hours = 750 * 40 * 52 = 1,560,000. With 6 accidents: AFR = (6 / 1,560,000) * 1,000,000 = 3.85 per million hours.
Example 3 — OSHA TRIR. 4 recordables, 410,000 hours.
TRIR = (4 / 410,000) * 200,000 = 1.95.
Why does the base matter? The base only rescales the rate. A TRIR of 2.0 per 200,000 hours equals an AFR of 10.0 per 1,000,000 hours. Both describe the same safety performance.
Should I include contractors? Include contractor cases and contractor hours together, or exclude both. Mixing the two will distort the rate.
What hours count? Only hours actually worked. Do not include vacation, sick days, or holidays. Salaried staff without time records are typically counted at 2,000 to 2,080 hours per year.
Is a lower number always better? Yes, mathematically. But very low rates can also signal under-reporting. Pair frequency rates with leading indicators like near-miss reports and inspection findings.
