How is it that you calculate when a star will die? How do you do it?

Question: How is it that you calculate when a star will die? How do you do it?
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Asked by kristjana to Nick on 13 Mar 2014.
- Nick Wright answered on 13 Mar 2014:
  
  Stars die when they run out of fuel to burn in their cores, so usually we estimate how much fuel a star has left to burn and we calculate how fast the star is burning that fuel. So when we know those two numbers we can work out how long it will take the star to burn through all its fuel. The star will also change its appearance as it gets really close to dying, usually be getting redder and more luminous (it becomes a giant star), so that can also be a good clue.

Question: How is it that you calculate when a star will die? How do you do it?