# What is the minimum information required to calculate life expectancy from a cox regression model?

I have four beginner questions about Cox models and life expectancy. I am attempting to re-implement models from published coefficients.

1. To calculate the life expectancy (LE) of any given individual, what is the minimum information required?

2. Given a Cox-Proportional Hazard's model for mortality, covariate beta coefficients and the baseline hazard function for years 1-11. Is this enough to calculate LE?

3. The LE of a 20 year old should be ~80, do you need the baseline hazard function for 60+ years to calculate their LE based on their covariates?

4. Could LE be defined as the year where probability of survival falls below 0.5? How could you calculate this?

Question 3. Cox models often start at some time well after birth and evaluate survival subsequent to some defined time = 0 of study entry. You have no information about anyone who might have died prior to the opportunity to enter the study. Prior survival information is more or less irrelevant, except that anyone entering the study has necessarily survived up until that time and the age at study entry might be a useful covariate.