Half-Life Calculator

What is the Half-Life Calculator?

Calculate how much of a substance remains after radioactive decay. Half-life describes how long it takes for half of a substance to decay, and it applies to radioactive isotopes and many other decay processes.

How to use the Half-Life Calculator

1. Enter your initial amount, your elapsed time, your half-life.
2. Results update automatically as you type; you can also press Calculate.
3. Read the output: remaining amount, percent remaining, decay constant λ.
4. Use the 📊 chart to see the result visually, then copy or share it.

Formula and method

Worked example

With initial amount = 100, elapsed time = 10, half-life = 5, the Half-Life Calculator returns remaining amount: 25; percent remaining: 25.000%; decay constant λ: 0.138629.

Where the Half-Life Calculator helps in real life

A medical isotope has a 6-hour half-life. The calculator shows how much remains after 24 hours, which helps explain why some tracers are used soon after preparation.

A student is working on carbon-14 dating problems. Entering half-life and elapsed time confirms the remaining fraction.

Common mistakes to avoid

• Assuming decay stops after two half-lives.
• Mixing hours, days and years.
• Using linear decay instead of exponential.
• Rounding the fraction too early.

💡 Practical tip: After 10 half-lives, less than 0.1% of the original amount remains.

Tips for better results

• Keep time units consistent with half-life.
• Remember each half-life halves the remaining amount.
• Use the fraction to check against known decay tables.

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