Carbon Dating Calculator
Estimate the age of a sample from the percentage of carbon-14 remaining, using the 5,730-year half-life — and the reverse, the fraction left after a given age.
How old something is from how much carbon-14 it has left.
How the carbon dating calculator works
Living things take in carbon-14 at the atmosphere's level; after death the isotope decays with a half-life of 5,730 years while carbon-12 stays. Age = −(t½ ÷ ln 2) × ln(fraction remaining): 50% left means one half-life, 25% two. The method works to about 50,000 years, after which too little carbon-14 remains to measure.
Radiocarbon labs also calibrate against tree rings because atmospheric carbon-14 has varied; the calculator gives the uncalibrated ("radiocarbon") age.
Formula: age = −(5730 ÷ ln 2) × ln(N ÷ N₀)
Worked examples
| Inputs | Estimated age | Note |
|---|---|---|
| 25% remaining | 11,460 years | two half-lives: 11,460 years |
| 80% remaining | 1,845 years | about 1,845 years |
| 1% remaining | 38,069 years | 38,069 years — near the method's limit |
FAQFrequently asked questions
How far back does carbon dating work?
To roughly 50,000 years. Beyond that less than 0.25% of the original carbon-14 remains, below what labs can measure reliably.
Why do dates get calibrated?
Atmospheric carbon-14 has not been constant, so a raw radiocarbon age is converted to calendar years with calibration curves built from tree rings, corals and cave deposits.
What can be dated?
Anything that was once alive and exchanged carbon with the air: wood, charcoal, bone, shell, textiles, seeds. Rocks and metals cannot.
What is the difference between 5,730 and 5,568 years?
Libby's original half-life estimate was 5,568 years; the better value is 5,730. Labs still report "Libby" ages by convention and correct in calibration.
Where these figures come from
- IUPAC — Standard atomic weights (2021 conventional values) — the molar-mass table
- NIST — CODATA 2018 fundamental physical constants — Avogadro constant, gas constant, speed of light
- NIST Chemistry WebBook — thermochemical data
- CSIRO — Australia's national science agency
Last checked: September 2026. Atomic masses are the IUPAC conventional values; constants are CODATA 2018; equations are the standard textbook forms.