Short answer
Stellar lifespans range from a few million years for the most massive stars to many billions or even trillions of years for the smallest. The main factor is mass, and the surprising part is that heavier stars live shorter lives. Our Sun is expected to shine for roughly 10 billion years in total.
Why mass sets lifespan
A bigger star has more fuel, but its core is hotter and denser, so it burns through that fuel far faster. Luminosity rises steeply with mass, much faster than the fuel supply does. The result is that a star with several times the Sun’s mass lives for a small fraction of the Sun’s lifetime, while a small red dwarf sips its fuel slowly and is expected to outlast the current age of the universe many times over.
A simple star lifespan calculator
There is no single exact formula, but a common rule of thumb for main-sequence stars is:
Lifespan (in billions of years) ≈ 10 × M^-2.5
Here M is the star’s mass in multiples of the Sun’s mass. The exponent is approximate, and sources use different values depending on the mass range, so treat the result as an order-of-magnitude estimate.
| Mass (Suns) | Approximate main-sequence lifetime |
|---|---|
| 0.5 | about 55 billion years |
| 1 | about 10 billion years |
| 2 | about 1.8 billion years |
| 5 | about 180 million years |
| 10 | about 30 million years |
To use it, find the star’s mass, raise it to the power of -2.5 on a calculator, and multiply by 10. For very small stars (under about 0.3 solar masses) and very massive stars (above about 20 solar masses), real lifetimes depart from this curve, so be extra cautious there. Red dwarfs are expected to live for trillions of years, far longer than the universe has existed so far.
What a star does for most of its life
Roughly 90 percent of a star’s life is spent on the main sequence, steadily fusing hydrogen into helium in its core. During this long stable phase its brightness changes only slowly. The remaining time is spent in shorter, more dramatic stages once the core hydrogen runs low.
The lifespan of our Sun
The Sun is about 4.6 billion years old, so it is roughly halfway through its main-sequence life. In several billion years it should swell into a red giant. Estimates for the timing differ between models, so it is best to think of this as “billions of years from now” rather than a precise date.
How stars end, by mass
- Low-mass stars (like red dwarfs): Expected to fade slowly into white dwarfs, though none are old enough to have done so yet.
- Sun-like stars: Become red giants, shed their outer layers as a planetary nebula, and leave behind a white dwarf.
- Massive stars: End in a supernova, leaving a neutron star or a black hole.
Because the stars in a group formed at the same time, star clusters are a good place to see stars of different masses at different life stages. And if you are new to the basics, our pillar on how a star differs from a planet covers what a star actually is.
Limits of the estimate
Real stars vary in composition, rotation, and whether they have a close companion, all of which can alter their lifetimes. Mass loss through stellar winds also matters for large stars. The rule of thumb above is for teaching and rough comparisons, not research.
FAQ
Does a star with more mass live longer? No. More massive stars live shorter lives because they burn fuel much faster.
Can a star turn into a planet? No. A star may end as a white dwarf, neutron star, or black hole. Objects too small to fuse hydrogen, such as brown dwarfs, are that way from the start.
What is the lifespan of our star? About 10 billion years for the main-sequence phase, with roughly half already behind it.