Radioactive Half-Life Calculator
Remaining quantity after radioactive decay.
Enter your values
Enter the initial quantity in g.
Enter the half-life in years.
Enter the elapsed time in years.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Remaining quantity
- 29.8292 g
- Fraction remaining
- 29.829%
- Decay constant
- 1.2097e-4 per year
- Half-lives elapsed
- 1.75
Quick answer
N = N0 x 0.5^(t/half-life).
N = N0 (1/2)^(t/T)
At a glance
| What it does | Remaining quantity after radioactive decay. |
|---|---|
| Category | Science |
| Inputs needed | Initial quantity, Half-life, Elapsed time |
| Main output | Remaining quantity |
| Formula | N = N0 (1/2)^(t/T) |
| Cost | Free — no sign-up, no download |
How to use the Radioactive Half-Life Calculator
- 1Enter the initial quantity and the substance's half-life (5,730 years for carbon-14).
- 2Enter the elapsed time in the same units as the half-life.
- 3Read the remaining quantity and fraction left.
Inputs explained
- Initial quantity(g)
- Enter the initial quantity in g.
- Half-life(years)
- Enter the half-life in years.
- Elapsed time(years)
- Enter the elapsed time in years.
Worked example
Using the values the calculator loads with:
Inputs
- Initial quantity100 g
- Half-life5730 years
- Elapsed time10000 years
Results
- Remaining quantity29.8292 g
- Fraction remaining29.829%
- Decay constant1.2097e-4 per year
- Half-lives elapsed1.75
Frequently asked questions
What is carbon dating based on?
Comparing the remaining carbon-14 fraction in organic remains to estimate age using this formula.
Does half-life depend on amount?
No — half-life is constant regardless of how much material is present.
What do I need to enter into the Radioactive Half-Life Calculator?
Just 3 values: initial quantity, half-life, elapsed time. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Radioactive Half-Life Calculator work out the answer?
N = N0 x 0.5^(t/half-life). It applies the formula N = N0 (1/2)^(t/T) and shows the working so you can check each step by hand.
Is the Radioactive Half-Life Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.