Star Lifetime Calculator
How long a star burns hydrogen on the main sequence, from its mass — luminosity rises steeply with mass, so heavy stars live fast and die young — with what it becomes at the end.
Luminosity scales with roughly the 3.
How the star lifetime calculator works
Luminosity scales with roughly the 3.5 power of mass, but the fuel scales only with the mass itself, so lifetime goes as mass to the −2.5. A star twice the Sun's mass shines eleven times brighter and lives a fifth as long. The Sun's ten billion years is the anchor; a 20-solar-mass star gets about ten million; a red dwarf at a tenth of a solar mass outlives the current age of the universe many times over.
The exponent and the solar lifetime are inputs because both are approximations: the mass–luminosity slope is steeper for mid-mass stars and shallower at the extremes.
Formula: L ∝ M^a; τ ≈ τ☉ × M^(1 − a) (a ≈ 3.5)
Worked examples
| Inputs | Main-sequence lifetime | Note |
|---|---|---|
| Twice the Sun | 1.77 billion years | under two billion years |
| A red dwarf | 559.02 billion years | trillions of years |
| A blue giant | 5.6 million years | a few million years |
FAQFrequently asked questions
Why do massive stars live shorter lives?
Their cores are hotter and denser, so fusion runs far faster — luminosity grows roughly as the 3.5 power of mass while the fuel grows only linearly.
How long will the Sun last?
About ten billion years on the main sequence, of which 4.6 have passed. Then a red-giant phase of a billion years or so, and a white dwarf forever after.
What decides the fate?
Mass at the end. Below about eight solar masses the core becomes a white dwarf; above it, the core collapses in a supernova, leaving a neutron star or, above roughly twenty, a black hole.
Why are red dwarfs so long-lived?
They burn slowly and, being fully convective, they mix their whole hydrogen supply into the core. Lifetimes run to trillions of years — none has ever died.
How accurate is the power law?
To within a factor of two across most of the main sequence. The exponent is nearer 4 for stars around the Sun's mass and nearer 3 for the heaviest; adjust it if you know better.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Measurement Institute — Australia's measurement authority
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.