Half-life calculator
Fill in what you know and leave the unknown box empty — it works out whichever one is missing. Nothing is uploaded; the arithmetic happens in your browser.
The formula
N = N₀ × (½)^(t ÷ t½)
Where this usually goes wrong
Time and half-life must share a unit. After three half-lives an eighth remains, not nothing.
Worked example
After three half-lives, 100 g is down to 12.5 g.
Those numbers are already in the boxes above — press Work it out to see it, then change them for your own.
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