How long does the sun last?
Scientists generally say that our sun is a white dwarf and it is estimated that white dwarfs live approximately ten billion years. Our sun is about five billion years old so that leaves about five billion years left. It is estimated that the sun has used up about half of its hydrogen.
The older the sun gets the more it expands. It continues to run out of hydrogen and helium and as this happens the sun loses its brightness. The outer layers of the sun (after many phases) will begin to drift away and form a planetary nebula. All that is left is the core. It shrinks and cools and becomes much much smaller.
When all of this is said and done it will then be called a black dwarf which is another saying for dead star.
I assume you are asking about our sun and that you are asking how long it will last before it in some way "dies" at some point in the future.
Scientists believe that the sun has been around for something in the area of 4.6 billion years. They believe that it has enough of the elements that it burns to be able to keep burning in its current state for something like another 5 billion years. At that point, it is believed that it will become a red giant star and swallow the Earth...