Half-Life Calculator
Calculate radioactive decay — see how much of a substance remains after any time
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.
How to use the Half-Life Calculator calculator
- Enter the quantities you know, using the units shown on each field.
- Read the computed results — they update instantly as you type.
- Use the visual explanation to see how the quantities relate.
- Copy the page URL to share the exact calculation.
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]
Frequently asked questions
How does the Half-Life Calculator calculator work?
Enter the known quantities and the calculator applies the governing physical law or scientific formula to find the unknowns, stating the equation it used and the units of every result. Computations run at high precision.
When would I use the Half-Life Calculator calculator?
It suits physics and chemistry homework, lab work, engineering estimates, and any time you want to explore how changing one quantity affects the others in a well-defined scientific relationship.
How accurate are the results?
The formula itself is evaluated at 30 significant digits of precision. Keep in mind that idealized models — such as neglecting friction, air resistance or measurement error — bound the real-world accuracy more than the arithmetic does.
Can I share a specific calculation with someone else?
Yes. Every value you enter updates the URL, so copying the address bar and sharing the link reopens the exact same calculation for whoever clicks it.