How old is the universe?
The universe is about 13.8 billion years old. The most precise measurement, from the Planck satellite's map of the cosmic microwave background, gives 13.787 ± 0.020 billion years.
Key facts
| Age | 13.787 ± 0.020 billion years |
|---|---|
| Measured by | Planck satellite (ESA), 2018 results |
| Oldest light we can see | Cosmic microwave background, ~380,000 years after the Big Bang |
| Observable universe | ~93 billion light-years across |
| Galaxies | Hundreds of billions to ~2 trillion |
| Oldest known stars | 12–13+ billion years |
The universe is about
13,787,000,000 years
old, and it gets one second older every second: 4.35 × 1017 seconds and counting.
How do we know the universe is 13.8 billion years old?
Three independent methods agree:
- The afterglow of the Big Bang. The cosmic microwave background is light released about 380,000 years after the Big Bang. The European Space Agency's Planck satellite mapped it in detail, and fitting those maps to the standard model of cosmology gives an age of 13.787 ± 0.020 billion years.
- The expansion of space. Galaxies are moving apart. Running the expansion backwards gives a similar age, although measurements of today's expansion rate (the Hubble constant) disagree slightly, a puzzle known as the Hubble tension.
- The oldest stars. Nothing can be older than the universe. The oldest stars found, in globular clusters and in our galaxy's halo, are 12 to 13 billion years old, which fits.
The Methuselah star
HD 140283, nicknamed the Methuselah star, is a star 190 light-years away that once seemed older than the universe itself: early estimates put it at over 14 billion years. Better measurements bring it to about 12 to 14.5 billion years, within the uncertainty of the universe's age. It formed very soon after the first generation of stars.
How big is the observable universe?
About 93 billion light-years across. That is more than twice 13.8 billion because space has kept expanding while the light was travelling to us. The observable universe holds hundreds of billions, perhaps up to 2 trillion, galaxies and about 1080 atoms. The whole universe may be much larger, or infinite.
What was before the Big Bang?
Nobody knows, and it may not be a meaningful question. In the standard picture time itself begins with the Big Bang, so there is no "before", just as there is nothing north of the North Pole. Some theories propose a previous contracting universe that bounced, or an eternal inflating multiverse in which our Big Bang is one of many. None has been confirmed.
The age of everything, side by side
| Thing | Age |
|---|---|
| The universe | 13.8 billion years |
| The Milky Way (oldest parts) | about 13.6 billion years |
| The Sun and solar system | 4.57 billion years |
| The Earth | 4.54 billion years |
| The Moon | about 4.5 billion years |
| Life on Earth | at least 3.5 billion years |
| Dinosaurs extinct | 66 million years ago |
| Modern humans | about 300,000 years |
See all of it squeezed into one day on the Earth history clock.
Questions people ask
How old is the universe?
About 13.8 billion years. The most precise figure, from the Planck satellite, is 13.787 ± 0.020 billion years.
How do scientists know the age of the universe?
By measuring the cosmic microwave background, the light left over from the Big Bang, and fitting it to the standard model of cosmology. The expansion rate of the universe and the ages of the oldest stars give consistent answers.
Is anything older than the universe?
No. The Methuselah star (HD 140283) once seemed to be, but with today's measurements its age, about 12 to 14.5 billion years, fits inside the universe's age.
What was there before the Big Bang?
Science doesn't know. In standard cosmology time starts at the Big Bang, so there may be no "before". Bouncing universes and the multiverse are ideas, not established facts.
How big is the universe?
The observable universe is about 93 billion light-years across. Beyond that we cannot see, and the whole universe may be far larger or infinite.
Last updated October 23, 2026.