Half-Life Decay Calculator
Calculate half-life decay with explicit inputs and a worked example.
Formula
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
- Single exponential decay process; elapsed time and half-life must use the same units.
Example Calculation
- Initial amount: 100
- Elapsed time: 20
- Half-life: 10
100 units after 20 time units with half-life 10 leaves 25 units.
Frequently asked questions
How do I use this calculator?
Enter initial amount, elapsed time, half-life. The result updates automatically. Use Reset to restore the example values.
What method does it use?
remaining = initial × 2^(−elapsed/half-life). Single exponential decay process; elapsed time and half-life must use the same units.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.