Half-Life Calculator
Remaining = Initial × (1/2)^(Time elapsed ÷ Half-life)100×(0.5)^(20/10)=100×0.25=25 g
Free online tool
Half-Life Calculator
Enter the initial amount, time elapsed and half-life period.
Instant calculation
Half-Life Calculator
Enter the initial amount, time elapsed and half-life period.
Your result
Calculation
Your numbers stay in this browser. Nothing is uploaded or saved.
Three clear steps
How to use this calculator
- 01
Enter initial amount
Type the starting quantity.
- 02
Enter times
Type the time elapsed and the half-life period (same units).
- 03
See remaining amount
Calculate to see how much remains after decay.
The formula
How this calculation works
Exponential decay formula. Each half-life reduces the amount by half.
Check the method
Worked examples
Each example follows the same formula used by the calculator.
100 g, half-life 10 years, 20 years elapsed — remaining?
100×(0.5)^(20/10)=100×0.25=25 g25 g remainingCommon questions
Questions about this calculation
What is the Half-Life Calculator?
The Half-Life Calculator helps you calculate remaining quantity after radioactive decay or exponential decrease. Enter your values and select Calculate to get an instant result.
How is the result calculated?
Exponential decay formula. Each half-life reduces the amount by half.
Can you show an example?
Example: 100 g, half-life 10 years, 20 years elapsed — remaining? — 25 g remaining.
Is my data saved when I use the Half-Life Calculator?
No. All calculations run locally in your browser. Your inputs and results are never uploaded, stored or shared with anyone.
Is the Half-Life Calculator free to use?
Yes. The Half-Life Calculator is completely free. No account, sign-up or payment is required. It works on mobile, tablet and desktop.
Continue calculating