Interactive Risk of Harm Calculator

Timothy C. Hain, MD • Page last modified: March 7, 2021

See the "restrictions" page for a discussion about the meaning of this calculator.


The Risk of Harm Formula, as first published by the Canadian Cardiovascular Society (1992), was meant to quantify risk for drivers with sudden cardiac events. While there are many things one can criticize about this formula, nevertheless, it does provide way of thinking about acceptable risk.

RH = TD x V x SCI x AC.

The pre-filled numbers below are taken from the paper of Barbic (2014). You can put in your own numbers and press the red "update" button to compute the risk for an arbitrary situation that you have defined. If your risk of harm is greater than the "acceptable risk of harm" that you have configured below, the box will turn red. To put things into perspective, the risk of a crash in ordinary drivers (in Utah) was about 4%/year (Vernon et al, 2002)

Numbers for someone who faints or has a serious seizure once/year are shown in the example below. The changes from standard are that the risk of incapacitation becomes 1, and the probability of a serious event also becomes 1. These are pretty reasonable numbers for someone who loses consciousness for 5 minutes, such a from a seizure or cardiac event. These two changes increases risk very substantially. Imagine then if someone is having 1 seizure every 3 months. The literature suggests that persons with seizures have roughly twice as many crashes/year as do persons without seizures (Vernon et al, 2002).

This calculator is presented to explain how the Risk of Harm Formula works. It is not intended for practical use as real world decisions may depend on other factors. For example, someone driving a bus or flying a plane risks all of the passengers, which would then greatly multiply the risk to society. Someone driving with their loved ones might want to take less risk than someone driving by themself.

Risk of Harm from Canadian Cardiovascular Society (2002) Accidents/year you are personally willing to accept
0.00005 = 1 serious accident or injury/20,000 years of driving 1 serious accident or injury per 20000.0 years of driving


Group Driving Time (TD) Fraction of day Vehicle (V) Risk of incapacitation (SCI)/year Probability of serious or fatal accident (AC) for an SCI event Risk of Harm (RH)/year
Normal Driver 0.04 0.28 0.01 0.02 0.00000224 =1 accident every 446428.6 years
Commercial Driver 0.25 1 0.01 0.02 0.00005 =1 accident every 20000.0 years
Example once/year 0.04 0.28 1 1.0 0.0112 = 1 accident every 89.3 years
Your situation. 1.0 hours/day 0.000002 =1 accident every 446428.6 years

(c) 2017 Timothy C. Hain, M.D.