Radiocarbon Dating Calculator
Radiocarbon dating (Carbon-14 dating) is a radiometric technique for determining the age of organic materials up to about 50,000 years old. This calculator uses the standard radioactive decay half-life formula with the Cambridge half-life of 5,730 years for C-14, as adopted by IUPAC and used by NIST. Enter the fraction of C-14 remaining (as a percentage of the original, modern level) and the calculator returns the estimated age in years before present (BP). Note that laboratory-measured radiocarbon ages must also be calibrated against an atmospheric calibration curve (such as IntCal20) for calendar age.
Radiocarbon dating formula
t = (t1/2 / ln 2) x ln(N0 / N)
Where t is the age (years before present), t1/2 is the C-14 half-life (5,730 years per IUPAC), N0 is the original C-14 activity, and N is the current C-14 activity. The ratio N/N0 is expressed as a decimal fraction (pMC divided by 100).
Fraction remaining versus age
| C-14 Remaining (%) | Age (Years BP) | Half-lives |
|---|---|---|
| 100.00 | 0 | 0.00 |
| 50.00 | 5,730 | 1.00 |
| 25.00 | 11,460 | 2.00 |
| 12.50 | 17,190 | 3.00 |
| 1.00 | 38,099 | 6.64 |
| 0.10 | 56,779 | 9.92 |
Radiocarbon dating calculator: frequently asked questions
What is the half-life of Carbon-14?
The Cambridge half-life of Carbon-14, adopted by IUPAC and NIST, is 5,730 years (plus or minus 40 years). Some older literature uses the Libby half-life of 5,568 years, but 5,730 years is the currently accepted value.
What is the formula for radiocarbon dating?
The age is calculated using: t = (t(1/2) / ln(2)) * ln(N0 / N), where t is the age, t(1/2) is the half-life (5,730 years), N0 is the initial activity, and N is the current activity. Entering the fraction of C-14 remaining as N/N0 is the most common approach.
What does 'fraction remaining' mean?
Fraction remaining is the ratio of current C-14 activity to the original C-14 activity (when the organism was alive). Modern calibration standards set the original activity reference. Laboratories measure this ratio and report it as a percentage of modern carbon (pMC).
What is the maximum age range for radiocarbon dating?
Radiocarbon dating is reliable up to approximately 50,000 years. Beyond this, the C-14 levels are too small to measure accurately. For older materials, other radiometric methods such as potassium-argon or uranium-lead dating are used.
Why do radiocarbon dates need calibration?
Atmospheric C-14 levels have varied over time due to solar activity and other factors. Raw radiocarbon ages must be calibrated against a calibration curve (such as IntCal20) to convert to calendar years. This calculator gives uncalibrated (conventional) radiocarbon ages.
Official sources
- NIST (National Institute of Standards and Technology): Atomic Weights and Isotopic Compositions.
- IUPAC Commission on Isotopic Abundances: Periodic Table and Isotopic Data.
- National Ocean Sciences AMS Facility: NOSAMS Radiocarbon Dating.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.