What half-life does this calculator use?

It uses the Cambridge half-life of 5730 years, which is the currently accepted value for C-14 decay. Some older literature used the Libby half-life of 5568 years — multiply results by 1.029 to convert.

What does "fraction remaining" mean?

It is the ratio of C-14 atoms in your sample to those in a modern (living) reference standard — typically expressed as a decimal (0.75 = 75% of original C-14 still present). Labs usually report this as pMC (percent modern carbon) divided by 100.

Why can't I enter a fraction above 1.0?

A fraction greater than 1.0 would imply more C-14 than a modern standard, which is physically impossible for natural samples. Bomb-pulse contamination or lab error are the usual causes if a lab returns pMC > 100.

What is the practical dating range for C-14?

Roughly 300 to 50,000 years. Below 300 years the precision is limited by the bomb-pulse effect and calibration curve wiggles; above 50,000 years the remaining C-14 is too small to measure accurately.

Does this give a calibrated calendar date?

No. This tool gives a raw (conventional) radiocarbon age in years BP. Converting to a calibrated calendar date requires IntCal calibration curves (OxCal, Calib, etc.) because atmospheric C-14 has varied over time.

Carbon-14 Dating Calculator

Enter the fraction of C-14 remaining in a sample and get its estimated age in years using the standard radiocarbon decay formula.

Sample C-14 Fraction

Enter the measured C-14 remaining relative to a modern standard.

Fraction remaining (e.g. 0.50 for 50%)

Half-life convention

Quick examples

Estimated Age

Conventional radiocarbon age in years BP (before 1950).

Enter a fraction and click Calculate.

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Summary

This tool estimates the age of an organic sample by applying the radiocarbon decay equation to the measured fraction of C-14 remaining. It uses the accepted half-life of 5730 years (Cambridge half-life) and computes age as t = −8267 × ln(fraction). Results are in uncalibrated (conventional) radiocarbon years before present (BP) and do not account for reservoir corrections or calibration curves.

How it works

Enter the fraction of C-14 remaining in the sample (e.g. 0.50 for 50%).
Optionally switch to pMC mode to enter percent modern carbon (0–100) instead of a decimal fraction.
The calculator applies t = (5730 / ln 2) × ln(N₀/N) to compute elapsed time.
The result is displayed in years BP (Before Present, i.e. before 1950).
Margin of error expands at very low fractions (>50,000 yr) due to limits of measurement.

Use cases

Estimate the age of wood, charcoal, bone, or shell samples in archaeology.
Verify radiocarbon age results from a lab report using your own calculation.
Teach or study the mathematics of exponential radioactive decay.
Cross-check ages cited in geological or paleontological studies.
Explore how measurement precision affects the calculated date range.

Frequently Asked Questions

Last updated: 2026-06-15 · Reviewed by Nham Vu

Fraction remaining	—
Half-life used	—
Decay constant λ	—
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