Hubble Time Calculator
The Hubble time — one over the Hubble constant — and the actual age of a flat universe with matter and dark energy, from H₀ and the density parameters, with the Hubble distance and how the tension between H₀ measurements shifts the age.
If the universe had always expanded at today's rate, it would have started 1/H₀ ago: the Hubble time, 14 billion years at 70 km/s per megaparsec.
How the hubble time calculator works
If the universe had always expanded at today's rate, it would have started 1/H₀ ago: the Hubble time, 14 billion years at 70 km/s per megaparsec. Matter slowed the expansion early on and dark energy has sped it up since, and for a flat universe the correction is a closed formula in the two density parameters — about 0.96 for the standard mix, giving 13.5 billion years.
The Hubble constant itself is measured two ways that disagree by 8%, and the age moves with it.
Formula: t_H = 1/H₀; t₀ = (2 / (3 H₀ √Ω_Λ)) asinh(√(Ω_Λ / Ω_m)) (flat universe)
Worked examples
| Inputs | Age of the universe (billion years) | Note |
|---|---|---|
| H₀ = 70, standard densities | 13.467 | 13.5 billion years |
| The Planck value | 13.796 | 13.8 |
| Matter only | 9.313 | two thirds of the Hubble time |
FAQFrequently asked questions
What is the Hubble time?
One over the Hubble constant — the age the universe would have if it had always expanded at today's rate. It is the natural timescale of cosmology, about 14 billion years.
Why is the real age different?
Because the expansion rate has changed: gravity slowed it for the first several billion years and dark energy has accelerated it since. For the standard mix the two roughly cancel, leaving 96% of the Hubble time.
What is the Hubble tension?
The cosmic microwave background implies H₀ near 67; supernova distance ladders give 73. Nobody has found the error, and the difference is a 5% shift in the universe's age.
What does flat mean?
That the density parameters sum to one, which measurements confirm to within a per cent. The page normalises what you enter so the closed formula applies.
How old is the universe, then?
About 13.8 billion years on the Planck cosmology, 13.5 on H₀ = 70. The oldest stars are 13 billion, which is why an H₀ much above 75 is a problem.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G and the speed of light
- IAU 2015 Resolution B3 — nominal solar and planetary conversion constants — the astronomical unit, solar mass and planetary radii
- Royal Observatory Greenwich — the historic home of the prime meridian
Last checked: September 2026. Constants are CODATA 2018 (G, c) and IAU 2015 nominal values (solar and planetary parameters).