# How is life expectancy calculated?

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Are causes of death factored?

In: 0

Life expectancy takes the current death rate at each age and basically adds them up.

For example, suppose people lived a maximum of 10 years, and the death rates looked like this:

* Age 0: 20% death rate.
* Age 1: 1%
* Age 2: 1%
* Age 3: 1%
* Age 4: 2%
* Age 5: 4%
* Age 6: 8%
* Age 7: 16%
* Age 8: 32%
* Age 9: 64%
* Age 10: 100%

Then we could imagine a hypothetical population of people going through all these ages, and see where they die:

* Age 0: 20% of the 100% of original people die -> 20% die at age 0, and 80% live on.
* Age 1: 1% of the remaining 80% of the original total die -> 0.8% of the original total die at age 1, and 79.2% live on (I’m going to round to one decimal place from here out)
* Age 2: 1% of 79.2% of the original total die -> ~0.8% of the original total die at age 2 (technically 0.792), and 78.4% live on
* Age 3: 1% of 78.4% die -> ~0.8% die, 77.6% live on
* Age 4: 2% of 77.6% die -> 1.6% die, 76.1% live on
* Age 5: 4% of 76.1% die -> 3.0% die, 73.0% live on
* Age 6: 8% of 73.0% die -> 5.8% die, 67.2% live on
* Age 7: 16% of 67.2% die -> 10.7% die, 56.4% live on
* Age 8: 32% of 56.4% die -> 18.1% die, 38.4% live on
* Age 9: 64% of 38.4% die -> 24.6% die, 13.8% live on
* Age 10: All of the final 13.8% die.

And then we average out how long everyone lived. In this example, we get 0.2 * 0 + 0.008 * 1 + 0.00792 * 2 + … + 0.246 * 9 + 0.138 * 10 from each of the death amounts at each age, for a life expectancy of ~6.4 years.

It’s basically just a real time average of the age of death of people. Causes are factored in, because people die of *something* but it’s not like they are generally applying some sort of projection of people *might die* in the future, it’s more real time than that.

For example during the height of the COVID pandemic life expectancy was reduced because you had so many people dying all of sudden at a younger age than was previously normal, all those COVID deaths dragged the life expectancy down a couple of years despite the likely long term expectation that young people born today wouldn’t be likely to die in bulk from COVID in 2064

Are causes of death factored? Yes, but perhaps not how you’re asking. They’re inherently built in because life expectancy is based on actual lives, not the expected age a human body could live to if no outside forces were applied.

It should be noted that life expectancy is measuring the average age a person will likely live to based on their current age, though it’s usually quoted as life expectancy *from birth* (i.e. ~77 years old). Life expectancy [changes as you age](https://www.ssa.gov/oact/STATS/table4c6.html) because people have died at earlier ages than you, which affects life expectancy. For example, life expectancy from birth may be 77, but for a 77 year old life expectancy is 10 years. Made it to 87? Now it’s 5 years.

Another interesting metric is *death probability*. In the link above you’ll see its relatively high at birth (0.006%), then plummets, then reaches the probability at birth at around age 53.