Primary result
Remaining amount
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Amount left
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Remaining = initial × (1/2)^(time ÷ half-life)
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Exponential decay
Half Life Calculator
Estimate remaining amount after radioactive, chemical, or compound decay.
Half-lives elapsed
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Percent remaining
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Decay factor
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Status
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Half Life Calculator: Exponential Decay and Remaining Amount
A half life calculator is an exponential decay tool. If you know the starting amount and how long one half-life lasts, you can estimate how much remains after any amount of elapsed time. That makes the page useful for science classes, medicine timing, chemistry, and any other situation where a quantity falls by halves over time.
The nice thing about half-life math is that it is predictable. Every full half-life cuts the amount in half again, so the pattern is always the same even if the numbers are different. The calculator shows the remaining amount, the number of half-lives that have passed, and the percent still left so the decay is easy to read at a glance.
The Math: The Core Rule Explained
The Core Equation
Remaining = initial × (1/2)^(elapsed time ÷ half-life)
| Signal | Meaning | Use |
|---|---|---|
| Initial amount | Starting quantity | The base of the decay |
| Half-life | Time for one halving | Sets the decay speed |
| Elapsed time | Time passed | Determines how many halvings occurred |
Real-World Use Case
A student can check homework or lab numbers without manually applying the exponent every time.
A planning scenario becomes easy to compare: if the time doubles, how much less remains? The calculator answers that instantly.
Because the result is shown as both a quantity and a percentage, it is easier to understand how quickly the decay is moving.
Frequently Asked Questions
Why does the amount keep halving?
That is the definition of half-life decay: each half-life leaves half of the previous amount.
Can I use any unit?
Yes. The units just need to stay consistent across the inputs.
What if half-life is very small?
The calculator still works because it uses the exponent directly.
Is this only for radioactive material?
No. The same math works for many decay processes and diminishing balances.
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