# How we compute your life expectancy

Start with "life tables", which contain your base chance of dying each year. Modify the base chances by multiplying by a health risk factor, which is (1 + days-lost-per-year/365) for each of the hazards. For health benefits, similarly decrease the chance of death.

This gives your of dying at each age, and hence of living to that age. Averaging these give "life expectancy". The math is not hard. If you want more detail, see the references . The hard part is figuring the number of days lost or gained per year for different activities.

### I'ld walk a mile for a camel

The detailed numbers and calculations we used are given below. It is easiest to comprehend many of the health risks by converting them to a common basis: the number of miles you would need to walk a day to overcome the health risk. The following table relates distance walked to changes in life expectancy:

Assume people walk a mile in 20 minutes, and that each minute exercised gives two minutes increase in life expectancy. So:
1 mile = 40 minutes
1 foot = 0.00757 minutes = 0.4545 seconds
132 feet = 1 minute
2.2 feet = 1 second
1.5 miles = 1 hour
36 miles = 1 day
252 miles = 1 week
13,000 miles = 1 year

### Here are the detailed numbers

Current age (years):
Sex: to make up for being male: 2,700 days = 100,000 miles = 3.5 miles/day Too bad for us males!
Race (white?):
Income (dollars per year):
Married female: to make up for being married: 900 days = 30,000 miles = 2 mile/day while you are married
Married male: to make up for being unmarried: 1,800 days = 60,000 miles = 4 mile/day while you would have been married
Smoking: one cigarette = 12 minutes = 1/3 mile
Driving (miles per day):
• 1 in 100 people die in car crashes (50,000/year out of a population of 250,000,000 times 50 years life) so drivers live 1/2 year shorter (1/100 chance of losing 50 years) = 6,000 miles walked over life = 1/4 mile/day
• if one drives 10,000 miles/year = 30 miles/day each mile driven requires 1/120 mile = 50 feet walked
• note: if you park a block and a half from your work, and hence walk three blocks a day, that balances the risk of driving!
• Wear seat belt? cuts risk of death in half -> 25 feet walked/mile driven
Motorcycle?
Bicycle?
use street with bike lane: risk of being hit is 1/6 that of no lane
Wear helmet?
See the Helmet Resource Center
Sexual preference (M/F)
Number of unprotected sexual acts per month
• heterosexual
• homosexual
living in the city vs. the suburbs (risk of being shot)
- compare that to danger of commuting divide by income or race Weight (pounds):
Height (inches):
Fat consumption (% of calories):
Fruits and vegetables (servings per day):
Keep a handgun in the house:
Flying - commercial airline (miles per year):
Flying - hobby (miles per year):
Hang gliding (flights per year):

DISCLAIMER: Of course, the additive model used here is not correct. But it is a good first approximation; regardless of how many miles a day you walk, you should quit smoking!

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ungar@cis.upenn.edu