Radioactive Decay Calculator
⚛ Atomic & Quantum. Use the Radioactive decay formula to find nuclei left, starting nuclei, time, half-life: pick the value you want, type the others, and the answer updates as you go.
Pick the ○ next to the value you want to find, fill in the others, and it solves as you type.
What each letter means
| Quantity | Unit |
|---|---|
| Nuclei left | no unit |
| Starting nuclei | no unit |
| Time | s |
| Half-life | s |
Worked example
Find the nuclei left when Starting nuclei = 1000, Time = 15 s, Half-life = 5 s.
Using N(t) = N0(1/2)^(t/T1/2): Nuclei left = 125.
Frequently asked questions
What is the formula for Radioactive decay?
N(t) = N0(1/2)^(t/T1/2).
What do the letters stand for, and what units are used?
Nuclei left, Starting nuclei, Time in s, Half-life in s.
How do you calculate nuclei left?
Put the values into N(t) = N0(1/2)^(t/T1/2). For example, with Starting nuclei = 1000, Time = 15 s, Half-life = 5 s, nuclei left = 125.
Can I solve for a different value?
Yes. In the calculator above, pick the circle next to any value (nuclei left, starting nuclei, time, half-life) and fill in the others: it rearranges the formula for you.
