Science & Engineering

Radioactive Decay Calculator

Radioactive Decay Calculator uses an initial amount, half-life, and elapsed time to find how much of a sample remains and how much has decayed.

What this calculator does

The Radioactive Decay Calculator estimates your result instantly from the values you enter, using standard science & engineering formulas. Radioactive Decay Calculator uses an initial amount, half-life, and elapsed time to find how much of a sample remains and how much has decayed. 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.

Radioactive Decay Calculator

Result

—
Amount Remaining
—
Amount Decayed

About Radioactive Decay Calculator

Radioactive material shrinks by half every half-life, and this tool applies that exponential decay.

Give the starting amount, the half-life, and the elapsed time in the same time units, and it reports what remains and what has decayed.

Formula & Mathematical Calculation

Amount Remaining = f(Initial Amount, Half-Life, Elapsed Time)

Calculated according to standard science formulas implemented in the calculator core.

Calculation Example

For N0 = 1000, half-life = 8 and elapsed time = 24 (three half-lives):

remaining = 1000 × 0.524÷8 = 1000 × 0.125 = 125, so 875 has decayed.

Key Benefits

  • Applies exponential half-life decay for any number of half-lives
  • Reports both the remaining and decayed amounts
  • Also derives the decay constant lambda from the half-life
  • Half-life and time can use any consistent unit

How to Use this Calculator

  1. Enter the initial amount
    Type the starting quantity in the Initial Amount field.
  2. Enter the half-life
    Type the half-life in the Half-Life field.
  3. Enter elapsed time
    Type the elapsed time in the same units in the Elapsed Time field.
  4. Calculate
    Select Calculate to read Amount Remaining and Amount Decayed.

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

  • Radioactive Decay 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

Remaining amount equals the initial amount times 0.5 raised to the elapsed time divided by the half-life.

Any unit works as long as the half-life and elapsed time use the same one.

Yes, the interpretation includes lambda calculated as ln(2) divided by the half-life.

More half-lives elapse, so the remaining amount falls and the decayed amount rises accordingly.

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.