How does the Half Life Calculator work?

N(t) = N₀ × (½)^(t/t½) Then: After n half-lives: N = N₀ / 2ⁿ Then: Decay constant: λ = ln(2)/t½ ≈ 0.693/t½ Then: Mean lifetime: τ = 1/λ = t½/ln(2) ≈ 1.443 × t½.

Can you give an example of how to use the Half Life Calculator?

Example: Input 100g substance, half-life 10 years, after 40 years gives a result of 4 half-lives; N = 100/2⁴ = 6.25g remaining.

Is the Half Life Calculator free to use?

Yes — completely free with no registration, download, or subscription required. All calculations happen instantly in your browser.

How accurate is the Half Life Calculator?

Our Half Life Calculator uses verified mathematical formulas and is accurate to multiple decimal places. Results are calculated in real-time using the same methods used by professionals.

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Half Life Calculator

Half-Life

Decay Constant (s⁻¹)

A half-life calculator computes how much of a radioactive substance, drug, or any exponentially decaying quantity remains after a given number of half-lives.

Symbol	Name	Unit	Description
N	Remaining amount	original units	—
N₀	Initial amount	original units	—
t½	Half-life	time period	—

Substance	Half-life	Field
Carbon-14	5,730 yr	Archaeology
Potassium-40	1.25 billion yr	Geology
Iodine-131	8 days	Nuclear medicine
Caffeine	5 hours	Pharmacology
Aspirin	15 min (in blood)	Pharmacology

References

›Half-life — NRC

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