Frequently Asked Questions
Everything you need to know about the Half-Life Calculator.
How does the half-life calculator work?
Enter any 3 of initial amount, remaining amount, half-life, or elapsed time; it solves N = N0(1/2)^(t/t½) for the 4th.
Is it free?
Completely free, no sign-up, downloads, or limits.
Does it include common isotopes?
Yes, a preset dropdown of ~15-20 isotopes (Carbon-14, Uranium-238, Iodine-131, and more) auto-fills the known half-life.
Does it show the decay constant?
Yes, alongside the answer it shows the decay constant (λ) and mean lifetime (τ).
Is there a chart?
Yes, a decay curve plots remaining amount vs. time, with your solved point marked.
Does it show percent remaining?
Yes, in addition to absolute amounts.
Does it show the steps, including logs?
Yes, when solving for time or half-life, the logarithmic rearrangement is shown explicitly.
What if I enter more remaining amount than initial?
It's flagged as physically invalid, since decay can't increase the amount.
Is my data stored?
No; everything runs in your browser and isn't stored or sent anywhere.
Does it work on mobile?
Yes, fully responsive on all screen sizes.