Science Calculators
Half-Life Calculator
Enter an initial amount, half-life, and elapsed time to calculate how much remains after decay.
25.000 remaining
25.00% remaining, after 2.00 half-lives
Uses N = N₀ × (1/2)^(t/half-life). The default (carbon-14, 5,730-year half-life, 11,460 years elapsed = 2 half-lives) should leave exactly 25% remaining.
How to use this tool
- 1Enter the initial amount.
- 2Enter the half-life.
- 3Enter the elapsed time (same units as half-life).
- 4See the remaining amount and percentage.
Frequently asked questions
Does this only apply to radioactivity?+
No — the same exponential decay math applies to drug elimination, capacitor discharge, and any process where a quantity halves at a constant rate.