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Calculators / Math / Half-life decay
Half-life decay calculator
Calculate remaining quantity after elapsed time using a half-life.
On this page
Remaining quantity18.95
Fraction remaining18.95%
Calculator controls
How to calculate
Calculate remaining quantity after elapsed time using a half-life.
Remaining quantity = initial*(1/2)^(time/halfLife); Fraction remaining = (1/2)^(time/halfLife)*100
Worked example
Initial quantity: 100; Half-life: 5; Elapsed time: 12.
Remaining quantity: 18.95 ; Fraction remaining: 18.95 %.
Assumptions and limits
The model assumes exponential decay with a constant half-life and no new material added.
Results are rounded for display; calculations use unrounded values. Read our calculation methodology.
Understanding the result
Calculate remaining quantity after elapsed time using a half-life. The displayed figures use the inputs and formula shown on this page.
When this tool is useful
Use the half-life decay to compare a scenario, check an estimate, or verify a manual calculation.
Understanding your inputs
| Input | What to enter |
|---|---|
| Initial quantity | Enter a number of at least 0 and no more than 1000000000000. |
| Half-life | Enter a number of at least 0.000001 and no more than 1000000000000. |
| Elapsed time | Enter a number of at least 0 and no more than 1000000000. |
Frequently asked questions
What should I check before using the half-life decay result?
The model assumes exponential decay with a constant half-life and no new material added.
Is this half-life decay result exact?
It is exact for the stated mathematical model and entered values. Real-world results can differ when rates, timing, fees, definitions or measurement conditions differ.