As a white male, my official life expectancy is 76 years. Let's say that there was some behavior I could engage in that would increase my productivity now but would decrease my life expectancy to 71 years. What is the present value of those five years? Here are my calculations (they shouldn't necessarily be trusted).
We'll assume a 10 percent discount rate. The present value of the five years of life from 71 to 76 in the year when I'm 71 is (1 / 0.1) * (1 - 1 / (1 + 0.1)^5) = 3.79 years. I'm 23, so the present value today of 3.79 years when I'm 71 is 3.79/(1.1^(71 - 23)) = 0.039 years, or two weeks.
So if a 10 percent discount rate is reasonable, and if the value of each year of life is constant, and if I'm perfectly altruistic, I should be indifferent to an extra two weeks of productivity now and an extra five years of productivity at the end of my life.
Is this correct?
A couple of decisions to which this sort of reasoning might apply:
* Choosing a high-stress career. Your life expectancy would be reduced, and you might have to retire early, but it could be worth it.
* Using nicotine gum or lozenges as a stimulant. This would increase your productivity now, but would increase your risk for cardiovascular disease later in life.
Can you think of any others?