Radiocarbon Dating Calculator (Carbon 14 Dating)
Estimate how long ago an organic sample stopped exchanging carbon with the atmosphere. This carbon dating calculator uses the remaining carbon-14 percentage and the isotope half-life to return elapsed time.
Estimated Age
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What This Carbon Dating Calculator Helps You Estimate
Radiocarbon dating works because living organisms continually exchange carbon with their environment. After death, that exchange stops and the carbon-14 fraction begins to fall in a predictable exponential pattern.
This calculator gives the clean mathematical estimate from the decay law. It is useful for intuition, classroom problems, and quick checks before you look at full calibration-based dating methods.
How to Calculate Carbon Dating Age
- Enter the carbon-14 percentage left: Use the measured percentage of modern carbon-14 remaining in the organic sample.
- Keep or adjust the half-life: The calculator defaults to the accepted carbon-14 half-life of 5,730 years.
- Run the calculation: The logarithmic decay formula converts the remaining fraction into elapsed time.
- Read the result as an estimate: Real radiocarbon dating also uses calibration curves and lab corrections, so this result is a simplified age estimate.
Because the formula is logarithmic, the age rises quickly as the remaining percentage gets small. That is why very old samples are harder to estimate precisely.
Radiocarbon Dating Calculator (Carbon 14 Dating) Formula
| Variable | Meaning | Unit |
|---|---|---|
| t | Time elapsed since the sample stopped exchanging carbon | years |
| t1/2 | Half-life of carbon-14 | years |
| C14_left_percent | Percentage of original carbon-14 remaining | percent |
The page converts the half-life into years before reporting the result, so you can compare carbon-14 percentages on a familiar archaeological timescale.
Worked Examples
- C-14 left: 50%
- Half-life: 5,730 years
Result: Age = 5,730 years
One half-life has passed, so the age equals the half-life itself.
- C-14 left: 25%
- Half-life: 5,730 years
Result: Age = 11,460 years
Two half-lives have passed because the remaining fraction is one quarter of the original amount.
- C-14 left: 12.5%
- Half-life: 5,730 years
Result: Age = 17,190 years
Three half-lives have passed, so the estimated age is three times 5,730 years.
Radiocarbon Dating Reference Table
| Range | Meaning | Action |
|---|---|---|
| More than 50% left | The sample is younger than one carbon-14 half-life. | Expect an age below about 5,730 years before calibration adjustments. |
| 12.5% to 50% left | The sample is between one and three half-lives old. | Ages fall in the broad archaeological range where radiocarbon dating is often useful. |
| Less than 12.5% left | The sample is relatively old and the signal is much weaker. | Interpret the estimate carefully because measurement uncertainty grows as carbon-14 becomes scarce. |
Frequently Asked Questions
Related Calculators
References
Last reviewed: March 14, 2026