Method
Remaining amount N(t) = N₀ × (1/2)^(t / half-life). The elapsed-to-half-life ratio counts completed and partial half-lives.
Math worksheet
Half-Life Calculator
Model exponential decay from an initial amount, half-life and elapsed time, with a stepwise decay table and Chart.js curve.
The calculation runs locally. Exact-integer tools avoid floating point; decimal and transcendental tools report rounding limits.
Method and verification guide
How the Half-Life Calculator works
Remaining amount N(t) = N₀ × (1/2)^(t / half-life). The elapsed-to-half-life ratio counts completed and partial half-lives. The calculator keeps the intermediate values visible so you can reproduce the answer independently.
Interpret the result
Every full half-life halves the current amount, not the original amount.
Check the assumptions
This assumes a constant exponential decay rate and no replenishment, production or multi-phase kinetics.
Local calculation
Everything runs in this browser. Inputs are not sent to an external calculator.
Rounding
Displayed values may be rounded for readability while calculations use full floating-point precision unless the tool explicitly uses exact integers.
Scope
This assumes a constant exponential decay rate and no replenishment, production or multi-phase kinetics.
Simple by design
Three steps to a clearer number.
Enter your details
Use realistic values in each field. You can change them anytime.
Calculate instantly
The formula runs locally, so there is no account or waiting time.
Use the result
Treat the answer as a practical estimate for your next decision.