Science
Half-life calculator
Initial amount, half-life and time → remaining amount.
- Instant
- Free
- Private (processed locally)
- No sign-up
Calculate the remaining amount
Enter the initial amount, the half-life and the elapsed time (half-life and time in the same unit). The tool applies exponential decay.
How it works
- 1 half-life → 50% remaining
- 2 half-lives → 25%
- 3 half-lives → 12.5%
- n half-lives → (1/2)ⁿ
Example
| Input | Value |
|---|---|
| Initial amount | 100 |
| Half-life | 10 |
| Elapsed time | 30 |
| Remaining | 12.5 (12.5%) |
100% local calculation, no data sent.
Frequently asked questions
What is the formula?
Remaining = initial × (1/2)^(t / T), where t is the elapsed time and T the half-life (same unit).
Example?
Initial 100, half-life 10, time 30 → 100 × (1/2)³ = 12.5.
What is a half-life?
It is the time after which half of the substance has decayed.
Does it work beyond radioactivity?
Yes: the same model fits pharmacokinetics (drug elimination), for instance.