Half-Life Calculator
Remaining amount after any number of half-lives.
Enter your values
Results update instantly as you type — no submit needed.
Results
- Amount remaining
- 25
- Fraction remaining
- 25%
- Half-lives elapsed
- 2
- Decay constant λ
- 0.00012097
- Mean lifetime
- 8266.6426
Working
- 1N = 100 × 0.5^(11460 ÷ 5730) = 25
Quick answer
After each half-life, half the remaining substance decays: N = N₀ × (1/2)^(t/T).
N = N₀ × (½)^(t ÷ t½)
How to use the Half-Life Calculator
- 1Enter the starting amount.
- 2Enter the half-life and elapsed time in the same units.
- 3Read the remaining amount.
Frequently asked questions
What is carbon-14 dating?
C-14 has a 5,730-year half-life, so measuring how much remains in organic material dates it back roughly 50,000 years.
Does half-life change with amount?
No. Radioactive decay is first-order, so the fraction lost per unit time is constant regardless of quantity.