Half-Life Calculator
Enter a starting amount, half-life, elapsed time and an optional repeat-dose interval to calculate amount remaining and decay milestones.
Result
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Amount remaining
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- Percentage remaining
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- Elapsed half-lives
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- Time to target
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| Half-lives | Amount | Percent |
|---|
This is generic first-order decay maths, not dosing advice.
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How the half-life calculator works
This half-life calculator uses exponential decay to estimate how much of a starting amount remains after elapsed time. Convert the half-life and elapsed time to the same unit, then apply the number of half-lives that have passed.
The table shows the percentage remaining after one through five half-lives: 50%, 25%, 12.5%, 6.25% and 3.125%. After five half-lives, roughly 97% has been eliminated, a common rule of thumb for effectively cleared.
The optional repeat-dose result applies the supplied interval to a generic steady-state accumulation formula. Clearance varies between people, and dosing decisions belong to a prescribing clinician.
Remaining = initial × 0.5^(time ÷ half-life) Half-life calculator FAQ
What does half-life mean?
Half-life is the time used in this maths model for an amount to fall to 50% of its previous amount.
Why must the time units match?
The calculator converts minutes, hours and days to a common unit before dividing elapsed time by half-life.
What does the time-to-target result show?
It uses halfLife × log2(initial ÷ target) to estimate the time for the amount to fall to the target you enter.
What is the optional repeat-dose result?
It estimates a generic steady-state accumulation factor and peak using the interval you supply. It is not a recommended schedule or dose.
Does this predict clearance for a person?
No. This is generic first-order decay maths. Clearance varies between people, and dosing decisions belong to a prescribing clinician.