Half-Life Calculator
Free online half-life calculator for radioactive decay and exponential decay. Solve for remaining quantity, initial amount, half-life, or elapsed time. Includes isotope presets (C-14, I-131, Co-60, U-238) and a decay timeline. 100% client-side.
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What is Half-Life Calculator?
The Half-Life Calculator is a free online tool for radioactive decay and exponential decay calculations. Using the universal decay formula N = N₀ × (1/2)^(t/t½), it solves for any one of four quantities — remaining amount, initial amount, half-life, or elapsed time — given the other three. It includes quick-select presets for common isotopes like Carbon-14 (5730 years), Iodine-131 (8.02 days), Cobalt-60, Uranium-238, and Radon-222, shows the full formula with your values substituted, and displays a decay timeline table so you can see how much material remains after each successive half-life. All calculations run entirely in your browser with no data sent anywhere, making it ideal for nuclear physics homework, radiocarbon dating problems, and pharmacokinetics calculations.
Key Benefits
- Solve for any of the four decay variables — not just the remaining quantity
- Built-in presets for common isotopes speed up radiocarbon dating and nuclear physics work
- Full worked formula with substituted values lets you verify the math and learn the equation
- Decay timeline table gives a visual reference of quantity after each half-life
- 100% client-side — works offline, no sign-up, and inputs never leave your device
Common Use Cases
- •Radiocarbon dating: estimate the age of archaeological samples from remaining Carbon-14
- •Nuclear physics homework: solve decay problems for any isotope or element
- •Pharmacokinetics: calculate drug elimination and dosing intervals from elimination half-life
- •Radiation safety: estimate remaining activity of radioactive sources over time
- •Environmental science: model the decay of radioactive contaminants in soil and water
How to Use the Half-Life Calculator
- Choose What to Solve: Click one of the four buttons at the top to select whether you want to find the remaining amount (N), initial amount (N₀), half-life (t½), or elapsed time (t).
- Enter Known Values: Fill in the three known quantities. For example, enter the initial amount, half-life, and elapsed time if solving for the remaining amount.
- Use an Isotope Preset (Optional): Click a common isotope button like Carbon-14 (5730 years) or Iodine-131 (8.02 days) to auto-fill the half-life field instantly.
- Read the Result: The answer appears instantly with the full formula showing your substituted values. Check the decay timeline table to see how much remains after each half-life.
Key Features
- Solves for any of four variables: remaining amount, initial amount, half-life, or elapsed time.
- Built-in presets for common isotopes — Carbon-14, Iodine-131, Cobalt-60, Uranium-238, and Radon-222.
- Shows the full decay formula N = N₀ × (1/2)^(t/t½) with your values substituted and verified.
- Interactive decay timeline table showing quantity and percentage across 0–6 half-lives.
- Handles extremely large or small numbers with exponential notation automatically.
- 100% client-side — works offline, no sign-up, and your inputs never leave your device.