Science
Half-Life Calculator
Use this half-life calculator for chemistry, physics, biology, and exponential decay homework.
Choose the missing quantity; the calculator hides that field and solves it from the others.
Solved value
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- Remaining amount
- —
- Initial amount
- —
- Elapsed time
- —
- Half-life
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Student quick launch
Grade planning, algebra checks, and formulas students reach for most.
Study path
Use this calculator with
Follow these when you want the formula behind the answer, a short lesson, or nearby tools in the same topic.
What the half-life calculator solves
Use this half-life calculator for chemistry, physics, biology, and exponential decay homework.
Formula
How to use it
- Choose the quantity you want to solve for.
- Enter the known values with consistent units.
- Check the rearranged formula, substitution, and warnings before using the result.
How to read the answer
After each half-life, the remaining amount is cut in half under the model.
Common mistakes and edge cases
- Use matching time units for elapsed time and half-life.
- This model assumes a constant decay rate.
- Do not use the time-solving mode when the amount has not decreased.
Worked examples
Find remaining amount
Solved value
Remaining amount = 25 units
Find elapsed time
Solved value
Elapsed time = 18 time units
Frequently asked questions
Can the half-life calculator solve for a missing variable?+
Yes. Use the solve-for control to hide the missing value, then enter the other known values with compatible units.
Why do the units matter?+
Formula calculators assume the entered values are already in matching units. Convert first when your measurements use mixed systems.
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Last updated: May 15, 2026