How this calculator works
The DART rate counts serious work injuries: cases that kept an employee away from work, or left them on restricted duty or transferred to another job. It is one of the rates US employers record under the OSHA injury and illness rules, and it is used to compare workplaces of different sizes. The raw count of injuries depends on how many people work somewhere, so the rate normalises it: the number of DART cases is divided by hours worked and multiplied by 200,000. That base represents 100 employees working 40 hours a week for 50 weeks, so the answer reads as the number of cases per 100 full-time workers per year. This calculator can also reverse the formula: given a target rate and the hours, it finds how many cases that implies, or how many hours a company with a given number of cases must have worked to reach the rate. The rate is only as good as the recordkeeping. Cases that should have been logged are missed, especially in small workplaces without a safety officer, and a change in reporting habits can move the rate without any change in safety. Compare a workplace with its own history and with similar workplaces, not with an arbitrary target.
Formula
DART rate = (number of DART cases x 200,000) / hours worked. Cases = rate x hours / 200,000. Hours = cases x 200,000 / rate. The 200,000 constant is 100 full-time equivalents x 40 hours x 50 weeks.
Worked example
A site with 4 DART cases across 500,000 hours has a rate of 4 x 200,000 / 500,000 = 1.6 cases per 100 full-time workers per year. At a target rate of 2.0, the hours worked would need to be 4 x 200,000 / 2.0 = 400,000 for the same four cases. A rate of 1.6 with 250,000 hours implies 1.6 x 250,000 / 200,000 = 2 cases.
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Frequently asked questions
What counts as a DART case?
A recordable injury or illness that results in days away from work, restricted work or transfer to another job. Ordinary recordable cases without those consequences count in the TRIR but not in the DART rate.
Why is the constant 200,000?
It is the number of hours 100 full-time workers work in a year at 40 hours a week for 50 weeks. Multiplying by it turns a ratio into cases per 100 full-time equivalent workers, which is easier to compare.
How do DART and TRIR differ?
TRIR counts all recordable cases, including those that needed only first aid beyond the recordable threshold and medical treatment. DART counts only the more serious cases involving lost or restricted workdays. DART is therefore always lower than or equal to TRIR.
Should I include contractor hours?
Only if the contractors are under your supervision and included in your OSHA log. Mixing them inconsistently between years makes the trend meaningless. Choose a rule and keep it.