Half-Life Calculator
Solve for remaining quantity, initial quantity, elapsed time, or the half-life itself.
| Nâ‚€ (Initial) | 100 |
| N (Remaining) | 25 |
| Half-Life | 5,730 |
| Elapsed Time (t) | 11,460 |
The Half-Life Formula
Half-life describes how long it takes for a decaying quantity - like a radioactive isotope - to fall to half its original amount. Because the decay follows the same fixed ratio every half-life period, the amount remaining after any elapsed time can be found with one exponential formula, and that same formula can be rearranged to solve for any of its four variables.
N = remaining quantity, N₀ = initial quantity, t = elapsed time, t½ = half-life
Common Examples
Carbon-14 (used in archaeological dating) has a half-life of about 5,730 years. Many medications and caffeine also follow this same exponential-decay pattern in the body, just on a much shorter timescale.