INCIDENT RATES · US OSHA METHOD
How to calculate DART rate
DART is a case rate, not a count of days lost. Start with the right cases, match their hours and period, then calculate.
By HSECalc · Published and references checked
1. Count cases, not days
DART covers recordable cases involving days away from work, restricted work or job transfer. For a completed OSHA 300 Log, use the case totals in columns H and I. OSHA describes this method in its Field Operations Manual, Chapter 3.
One case that involves both absence and later restricted work contributes one case to DART. Do not add it twice. The days-away and restricted-day totals are different fields from the case classifications.
A classification needs to follow the applicable recording rules. OSHA 1904.7 explains how to handle days away, restricted work and transfers. The calculator does not determine whether an event is work-related or recordable.
Pair the case count with employee hours actually worked for the same workforce and reporting period. Use the OSHA forms and instructions when assembling the records. A headcount or paid-hours total is not automatically the correct denominator.
2. Work through an example
The 200,000-hour base represents 100 full-time equivalent workers. Keep the base fixed and enter your own hours.
In this fictional example, one site has 2 cases with days away, 1 separate case with restriction or transfer, and 300,000 hours worked for the period.
- Add the distinct cases: 2 + 1 = 3.
- Multiply by the base: 3 × 200,000 = 600,000.
- Divide by the hours: 600,000 ÷ 300,000 = 2.00.
Report a DART rate of 2.00 with the reporting period, site, case count and hours. This is not 2% of workers, and it does not mean two days were lost.
Check your figures in the DART calculator ↗DART and TRIR answer different questions
| Measure | Case group | What to avoid |
|---|---|---|
| DART | Cases involving days away, restriction or transfer | Entering the total number of days |
| TRIR | Total recordable cases, including categories outside DART | Using only the DART case count |
If the example also has 2 other recordable cases, TRIR uses 5 cases: (5 × 200,000) ÷ 300,000 = 3.33. DART remains 2.00. That difference is expected, not a calculation error. Read the TRIR worked-example guide or use the TRIR calculator.
Read the result before choosing an action
A DART rate describes recorded case experience. It does not establish that a job is safe or measure every hazard. Compare only compatible data, and investigate what happened rather than treating a colour or score as a complete assessment.
For trend reporting, keep a note of the method, scope and source records. Review prevention measures and whether corrective actions worked. OSHA's incidence-rate interpretation discusses why small workforces need context and why multiple indicators matter.
Common questions
Does a case with days away and restricted work count twice?
No. Count the distinct recordable case once in the DART numerator. If you are using a completed log, use its case-classification totals rather than adding individual days.
Should I enter calendar days away?
No. The rate needs a case count. Day-counting rules matter when completing the log, but the resulting number of days is not the DART numerator.
Can I calculate a monthly DART rate?
The arithmetic works with cases and hours for the same month. Keep the 200,000 base and label the period. A short period can fluctuate sharply, so do not treat it as directly equivalent to a full-year comparison.
Can I combine monthly rates by averaging them?
Add their distinct case totals and hours first, then calculate one rate. For example, 1 case in 50,000 hours and 2 in 250,000 hours combine to 3 cases in 300,000 hours: DART 2.00. Averaging the separate rates, 4.00 and 1.60, would give the wrong combined answer.
Does DART replace UK or other national reporting?
No. This guide explains a US-method KPI. Keep local statutory reporting duties and definitions separate from this calculation.
Original references
- OSHA Field Operations Manual, Chapter 3 — DART definition, case columns and formula.
- OSHA 1904.7 — general recording criteria and case outcomes.
- OSHA recordkeeping forms — log, annual summary and instructions.
- OSHA incidence-rate interpretation — fixed base and interpretation limits.
Independent educational guidance; not endorsed by OSHA. Report an error or unclear example.