Caption: In the adjacent image, we calculate the Sun's main sequence lifetime to be ∼ 10 Gyr making use of the fact that the Sun only burns about 10 % of its hydrogen. This means it has a hydrogen burning efficiency factor f_☉ = 0.1 which is a fiducial value, NOT an exact value.
Both the fiducial and more exact efficiency factors f_☉ can, in fact, only be known by stellar structure modeling.
Then it will become an asymptotic giant branch (AGB) star and lose much of its outer layers in thermal pulses (AKA helium shell flashes). Then it will settle down as a white dwarf and cool off forever (see Wikipedia: Sun: After core hydrogen exhaustion).