How to use the radioactive decay calculator
Find the amount remaining after radioactive decay. Enter initial amount, half-life, elapsed time in the fields above; the remaining amount, fraction remaining, decay constant are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- N0 — Initial amount
- th — Half-life (years)
- t — Elapsed time (years)
Worked example
With initial amount = 100, half-life = 5730 years, elapsed time = 10000 years, the calculator gives remaining amount ≈ 29.82924; fraction remaining ≈ 29.82924 %; decay constant ≈ 0.00012097 1/year.
Frequently asked questions
What is the formula for the radioactive decay calculation?
Remaining amount = N0 × 0.5^(t / th). Fraction remaining (%) = 100 × [Remaining amount] / N0. Decay constant (1/year) = ln(2) / th. Here N0 is initial amount, th is half-life (years), t is elapsed time (years).
What inputs do I need for the radioactive decay calculator?
You need initial amount, half-life in years, elapsed time in years. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.