How old is the universe? What the measurements say

The universe is about 13.8 billion years old. Using the standard model of the universe, data from the European Space Agency's Planck satellite give 13.797 billion years, with a stated uncertainty of 23 million years (Planck 2018 results). Adding maps of galaxies gives 13.787 billion years, give or take 20 million. NASA's earlier WMAP satellite found 13.77 billion years.

That number is not a guess. It comes from the oldest light in the universe, and it agrees with the ages of the oldest stars we can find.

The age counts the time since the universe's early hot, dense state, the Big Bang. These measurements do not tell us what, if anything, came before.

How old is the universe? About 13.8 billion years

Different teams, using different telescopes, arrive at almost the same answer:

The ± numbers show how sure each team is. Planck's uncertainty is less than 0.2 percent. Note that the first three rows are not separate checks: Planck and Planck-plus-BAO share the same data, and WMAP uses the same method, the oldest light. They all assume the standard model of the universe, called Lambda-CDM (Lambda stands for dark energy, CDM for cold dark matter).

The star-cluster method is different: it dates stars with models of how stars age, plus an estimate of when the first clusters formed. It is much less precise, but it does not rely on the oldest light, and it agrees.

How the oldest light reveals the age

About 375,000 years after the Big Bang, according to NASA, the universe had cooled enough for light to travel freely for the first time. That light is still arriving from every direction. It is called the cosmic microwave background.

The map above shows it: the colours are tiny temperature differences, fractions of a degree. NASA explains that WMAP's measurements of these differences reveal the size, matter content, age, geometry and fate of the universe.

The pattern of hot and cold spots depends on how much ordinary matter, dark matter and dark energy the universe contains and how fast it expands. When scientists find the mix that fits the map best, the age follows from it. Planck's best fit gives an expansion rate of 67.4 km per second per megaparsec (a megaparsec is about 3.26 million light-years) and says that matter makes up 31.5 percent of today's total matter-and-energy density, including both ordinary and dark matter.

Why the age isn't just 1 divided by the expansion rate

The universe is expanding: distant galaxies move away from us faster the farther away they are. The expansion rate (the Hubble constant) tells you how fast. Dividing 1 by today's expansion rate gives a useful timescale. It would equal the age only in a simplified universe whose expansion never sped up or slowed down.

With Planck's rate, that simple division gives about 14.5 billion years, not 13.8. The difference comes from history: gravity slowed the expansion at first, and now it speeds up. NASA calls the cause of that speeding up dark energy: in 1998 two teams found that distant exploding stars were dimmer than expected, and NASA says dark energy makes up about 68 to 70 percent of the universe, although nobody knows yet what it is.

We checked this ourselves. We calculated the age of a simplified flat universe with Planck's values (expansion rate 67.36, matter 31.53 percent, plus the tiny amount of radiation) and got 13.795 billion years, 1.8 million years lower than Planck's published 13.797.

The Hubble tension. Measurements of nearby galaxies give a faster rate. The SH0ES team, using the Hubble Space Telescope, found 73.04 ± 1.04 km/s/Mpc and reports a "5-sigma" difference with the value predicted by Planck and the standard model, meaning the gap is very unlikely to be chance. The Atacama Cosmology Telescope team, combining its data with Planck ("P-ACT"), CMB lensing and DESI DR1 BAO galaxy maps, found 68.22 ± 0.36, close to Planck. For illustration, using 73.04 while keeping the same matter fraction in our simplified model gives 12.7 billion years; that is not a measurement. How resolving this disagreement would change the age depends on the explanation.

Checking with the oldest stars

A completely different way to check the age: the universe must be older than its oldest stars.

Globular clusters are tight balls of hundreds of thousands of old stars, like Messier 4 in the photo. Astronomers can tell their age from how their stars have changed over time. A 2020 study by David Valcin and colleagues found that the oldest globular clusters are on average 13.32 billion years old (with an uncertainty of about half a billion years). Allowing for the time before those first clusters formed, they estimated the age of the universe at 13.5 billion years, with a similar uncertainty.

That is very close to Planck's 13.8 billion years, and it is based on stars rather than the oldest light. The two methods agree within their uncertainties.

The Methuselah star: older than the universe?

HD 140283 is a nearby old star nicknamed the "Methuselah star". In 2013, Howard Bond and colleagues used a precise distance from the Hubble Space Telescope to estimate its age at 14.46 billion years, with a total uncertainty of about 0.8 billion years. That looked older than the universe. The authors noted that within the errors it does not conflict with the age of the universe, but the star must have formed soon after the Big Bang.

Later studies came out younger:

• 2021: Jianling Tang and Meridith Joyce found about 12 billion years (± 0.5 billion), using new measurements of the star's size and updated models.
• 2024: C. Guillaume and colleagues found 12.3 billion years with models that use the star's own mix of chemical elements. With a solar-like mix, they got 14 billion years, which they describe as in tension with the age of the universe.

So the star is very old. Recent models using its measured properties give ages around 12 to 12.3 billion years, below the age of the universe, but the result depends on the modelling assumptions.

Is the universe 26.7 billion years old?

In 2023 Rajendra Gupta published a paper in the Monthly Notices of the Royal Astronomical Society proposing a different model of the universe. In that model, the universe would be 26.7 billion years old, which he argues could explain some very early galaxies seen by the James Webb Space Telescope. The paper compares this with the 13.7 billion years of the standard model.

The model drops parts of the standard picture: it combines "covarying coupling constants" (the idea that some constants of nature change over time) with "tired light" (the idea that light loses energy on its long journey). The 26.7-billion-year value is an inference from Gupta's alternative model, not a direct measurement. The standard-model estimates from the oldest light quoted here give about 13.8 billion years; the ages of the oldest stars are a separate consistency check, showing the universe is at least about 13 billion years old.

The universe in one calendar year

Big numbers are hard to picture, so we squeezed the universe's 13.797 billion years into one calendar year. Each day then stands for about 37.8 million years, and each second for about 438 years.

On this calendar, the final second of 31 December covers the last 438 years, and the Sun only arrives at the start of September. The planets you can find on our Tonight page formed with the Sun, so they are latecomers too.

How old is the universe? FAQ

How old is the universe? About 13.8 billion years. The Planck satellite measured 13.797 billion years, give or take 23 million.

How do we know how old the universe is? Mainly from the cosmic microwave background, the oldest light, which tells scientists how fast the universe expands and what it is made of. The ages of the oldest star clusters give an independent check: about 13.3 billion years for the clusters, so the universe must be at least that old.

How old is the Big Bang? The Big Bang happened about 13.8 billion years ago; the age of the universe is counted from it.

How old is the universe in years and in seconds? About 13,800,000,000 years, or roughly 4.35 × 10¹⁷ seconds (our calculation with 13.797 billion years).

Which is older, the Earth or the universe? The universe, by far. NASA puts the Sun's formation at about 4.6 billion years ago and Earth's at about 4.5 billion years ago, so the universe is about three times as old as Earth.

What is dark energy? NASA's short answer is "We don't know." It is whatever makes the expansion of the universe speed up, discovered in 1998 when two teams found that distant exploding stars were dimmer than expected. NASA says about 68 to 70 percent of the universe is dark energy.

Why do scientists keep changing the age? The value has barely moved recently: NASA's WMAP gave 13.77 billion years, Planck 13.797 billion. What is still debated is the exact expansion rate (the Hubble tension); how resolving it would change the age depends on the explanation.

Is anything older than the universe? No object has been established to be older than the universe. Some stellar age estimates come out higher, such as 14.46 billion years for HD 140283 in 2013, but uncertainties and modelling assumptions matter; recent models for that star give about 12 to 12.3 billion years.

How we checked

The age values come from the Planck Collaboration's 2018 cosmological parameters paper (Astronomy & Astrophysics 641, A6, Table 2: 13.797 ± 0.023 billion years from Planck alone, 13.787 ± 0.020 with BAO), NASA's WMAP mission overview (13.77 billion years "to within a half percent", light released about 375,000 years after the Big Bang) and Valcin et al. 2020 (JCAP, globular clusters). The star ages come from Bond et al. 2013, Tang & Joyce 2021 and Guillaume et al. 2024. The expansion rates come from Planck 2018 (67.4 ± 0.5), Riess et al. 2022 (SH0ES, 73.04 ± 1.04) and the Atacama Cosmology Telescope DR6 paper (Louis et al. 2025). The 26.7-billion-year model is from Gupta 2023. Dark energy, the Sun's age and Earth's age come from NASA.

Our own calculation: the age of a flat universe with matter, radiation and dark energy, from Planck's expansion rate (67.36 km/s/Mpc) and matter density (0.3153), integrated numerically. It gives 13.795 billion years against Planck's 13.797, 1.8 million years lower; our simplified calculation treats neutrinos as massless and does not reproduce every detail of Planck's analysis. The formula: age = ∫₀¹ da / (a·H(a)), with H(a) = H₀ √(Ωm a⁻³ + Ωr a⁻⁴ + ΩΛ), ΩΛ = 1 − Ωm − Ωr, radiation from a CMB temperature of 2.7255 K and an effective neutrino number Neff = 3.046 (Ωr = 9.206 × 10⁻⁵ for the baseline), solved numerically with Simpson's rule (20,000 steps). The "1 ÷ expansion rate" values (14.5 and 13.4 billion years), the illustration with a faster rate, the one-year calendar and the age in seconds are our calculations too. For the globular-cluster range in our chart we combined the stated statistical and systematic uncertainties in quadrature, which assumes they are independent.

The charts and the method diagram are our own. The images of Webb's First Deep Field, the WMAP sky and the Hubble Ultra Deep Field are from NASA (public domain); Messier 4 is by ESA/Hubble & NASA (CC BY 3.0, source). We resized them and cropped the cover. None of the images is AI-generated.