Half-Life Calculator
Remaining amount after any number of half-lives.
Enter your values
Enter the starting amount you are working with.
Enter the half-life in units of time.
Enter the time elapsed in same units.
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.
- 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)
At a glance
| What it does | Remaining amount after any number of half-lives. |
|---|---|
| Category | Science |
| Inputs needed | Starting amount, Half-life, Time elapsed |
| Main output | Amount remaining |
| Formula | N = N₀ × (½)^(t ÷ t½) |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Starting amount
- Enter the starting amount you are working with.
- Half-life(units of time)
- Enter the half-life in units of time.
- Time elapsed(same units)
- Enter the time elapsed in same units.
Worked example
Using the values the calculator loads with:
Inputs
- Starting amount100
- Half-life5730 units of time
- Time elapsed11460 same units
Results
- Amount remaining25
- Fraction remaining25%
- Half-lives elapsed2
- Decay constant λ0.00012097
- Mean lifetime8266.6426
- N = 100 × 0.5^(11460 ÷ 5730) = 25
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.
What do I need to enter into the Half-Life Calculator?
Just 3 values: starting amount, half-life, time elapsed. 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 Half-Life Calculator work out the answer?
After each half-life, half the remaining substance decays: N = N₀ × (1/2)^(t/T). It applies the formula N = N₀ × (½)^(t ÷ t½) and shows the working so you can check each step by hand.
Is the 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.