Half-Life Calculator
Calculate radioactive decay — see how much of a substance remains after any time
N = 100 × (1/2)^(11460/5730) = 25.0000
Remaining amount
25
Percent remaining
25%
Number of half-lives
2
About this calculator
The Half-Life Calculator determines how much of a radioactive substance remains after any given time. Enter the initial amount, half-life period, and elapsed time to see the remaining quantity and percentage. Useful for nuclear physics, radiocarbon dating, medical imaging, and understanding exponential decay.
Common examples
- N₀ = 100 g, T½ = 5 years, t = 10 years → 25 g remaining (25%)
- N₀ = 1,000 mg, T½ = 6 hours, t = 24 hours → 62.5 mg remaining (6.25%)
- N₀ = 50 g, T½ = 1,600 years, t = 3,200 years → 12.5 g remaining (25%) [radium-226]
- N₀ = 200 g, T½ = 8 days, t = 40 days → 6.25 g remaining (3.125%) [iodine-131]
- N₀ = 1 g, T½ = 5,730 years, t = 11,460 years → 0.25 g remaining (25%) [carbon-14]