Half-Life Calculator
Uses exponential decay N = N0 x 0.5^(t/half-life) to find how much of an initial quantity remains after a given elapsed time, plus the percent remaining.
What this calculator does
The Half-Life Calculator estimates your result instantly from the values you enter, using standard science & engineering formulas. Uses exponential decay N = N0 x 0.5^(t/half-life) to find how much of an initial quantity remains after a given elapsed time, plus the percent remaining. Calculations run in your browser, so nothing you type is sent to a server, and the output is an estimate rather than a certified or official figure.
Result
About Half-Life Calculator
This half-life calculator models exponential decay with N = N0 × 0.5^(t/T), where N0 is the initial quantity, T is the half-life, and t is the elapsed time. It reports both the remaining quantity and the percent of the original that is left.
The half-life and elapsed time just need to share the same time unit — seconds, years, or anything consistent — and the remaining amount is expressed in the same units as the initial quantity.
Formula & Mathematical Calculation
Remaining Quantity = f(Initial Quantity, Half-Life, Elapsed Time)
Calculated according to standard science formulas implemented in the calculator core.
Calculation Example
With an initial quantity of 100, a half-life of 5, and 15 time units elapsed, that is 15/5 = 3 half-lives. The remaining quantity is 100 × 0.5³ = 12.5, which is 12.5% of the original.
Key Benefits
- Computes remaining quantity from N = N0 times 0.5 raised to elapsed time over half-life
- Also reports the percent of the original amount still present
- Works with any consistent time unit for half-life and elapsed time
- Shows how many half-lives the elapsed time represents in the summary
How to Use this Calculator
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Enter the initial quantity
Type the starting amount N0 in the Initial Quantity field. -
Enter the half-life
Type the half-life in the Half-Life field, using your chosen time unit. -
Enter the elapsed time
Type how much time has passed in the Elapsed Time field, using the same time unit as the half-life, then press Calculate.
Assumptions & Limitations
What the calculation assumes
- Every value you enter is treated as an exact, known amount.
- Any rate or interval you enter is assumed to hold for the whole period unless the form asks for it separately.
- Results use standard published formulas and account only for the values entered above.
- Rounding is applied for display; the underlying calculation uses your full precision.
- Results are returned in the same units you enter, unless the tool states the output unit.
What it does not cover
- Half-Life Calculator produces a calculated result for reference and learning, not a certified or official measurement.
- Real-world outcomes differ when tolerances, rounding rules or local standards apply.
- Definitions and standards vary by region and change over time; verify the convention that applies to your case.
- Figures are only as accurate as the inputs you supply — check them before acting on the result.
- For work where the result carries real consequences, confirm it against an authoritative source.
Frequently Asked Questions
Free to use, no account needed. Calculations run in your browser, so nothing you type is sent to a server. Results are estimates — how we build and check our calculators.