Half Life Calculator · Practical guide
Carbon-14 Half-Life Calculator
Carbon-14 halves every 5,730 years — enter any age or amount to see how much of the original remains.
At a glance
The Carbon-14 Half-Life
Carbon-14 decays with a half-life of about 5,730 years. Living organisms keep their carbon-14 topped up from the atmosphere; once they die, the clock starts, and the remaining fraction reveals their age.
Interactive tool
Half Life Calculator
Enter your own values, then compare the result with the examples below.
Result
Worked Example
An artifact's wood contains 25% of the carbon-14 found in living wood. Since 25% means two half-lives have passed (100% → 50% → 25%), the sample is about 2 × 5,730 = 11,460 years old. Check the forward direction in the calculator above: enter an initial quantity of 100, a half-life of 5,730 years, and an elapsed time of 11,460 years — it returns 25 remaining, 75 decayed, and 2 half-lives passed.
Carbon-14 Decay Reference
| Elapsed Time | Half-Lives | C-14 Remaining |
|---|---|---|
| 5,730 years | 1 | 50% |
| 11,460 years | 2 | 25% |
| 17,190 years | 3 | 12.5% |
| 22,920 years | 4 | 6.25% |
The Limits of Radiocarbon Dating
Carbon-14 dating works reliably back to roughly 50,000 years — about 8-9 half-lives — beyond which less than 0.5% of the original carbon-14 survives and measurement noise takes over. Older material requires other isotopes, such as uranium-238 with its 4.5-billion-year half-life. Fractional ages work too: a sample 8,000 years old retains (0.5)^(8,000 ÷ 5,730) ≈ 38.0% of its original carbon-14.
Frequently Asked Questions
Why is the carbon-14 half-life 5,730 years?
It is a measured physical constant of the isotope. Laboratories determined it by tracking decay rates in known samples; the value is the same everywhere on Earth.
What can be dated with carbon-14?
Anything that was once alive: wood, bone, charcoal, shell, cloth. Rocks and metals cannot be radiocarbon dated because they never absorbed atmospheric carbon.
How accurate is carbon-14 dating?
Within its useful range, typically within decades to a few centuries, refined by calibration curves that correct for historical swings in atmospheric carbon-14.
Does this calculator work for other isotopes?
Yes — enter any half-life with its unit. For uranium-238 use 4.5 billion years; for iodine-131, a medical isotope, use about 8 days.