What Is a Half-Life Calculator?
Half-life is the time it takes for a quantity to reduce to half its original value — a concept from radioactive decay, but also used in pharmacology (drug elimination), chemistry, and finance. This calculator finds the remaining amount after a given time, or the half-life itself from known before/after amounts.
How to Use the Half-Life Calculator
- Choose whether to find remaining amount or the half-life.
- Enter the initial amount and known values.
- View the calculated result.
Half-Life Formula
Worked Example
15 ÷ 5 = 3 half-lives have passed
Remaining = 100 × (1/2)³ = 100 × 0.125 = 12.5
Understanding Your Results
Half-life decay follows an exponential curve — the quantity never reaches exactly zero, but keeps halving indefinitely (in theory). This same math applies whether you're modeling radioactive isotopes, drug concentration in the bloodstream, or any other exponential decay process.
Common Uses
- Radioactive decay and carbon dating in science and archaeology.
- Pharmacology: how quickly a drug is eliminated from the body.
- Chemistry: reaction rates for first-order reactions.
Frequently Asked Questions
The time it takes for a quantity to reduce to exactly half its original value, following exponential decay.
Divide elapsed time by the half-life to find the number of half-lives passed, then multiply the initial amount by (1/2) raised to that number of half-lives.
Mathematically, no — exponential decay approaches zero but never technically reaches it, though after many half-lives the remaining amount becomes negligible in practice.
Yes — it's used in pharmacology (drug half-life determines dosing frequency), chemistry (reaction kinetics), and other fields involving exponential decay.
Use the formula T½ = t × ln(2) / ln(N₀/N(t)), solving for the half-life from the initial amount, remaining amount, and elapsed time.