☢️Half-Life Calculator
Solve for initial amount, remaining amount, half-life, or elapsed time.
Runs entirely in your browser. No data is sent to a server.
Free Half-Life Calculator
Working through a radioactive decay or half-life problem? Our free half-life calculator solves for whichever value you're missing — initial amount, remaining amount, half-life, or elapsed time — using the standard exponential decay formula. Pick a common isotope like Carbon-14 or Uranium-238 from the preset list to auto-fill its known half-life, or enter your own.
Alongside the answer, you'll see the decay constant, mean lifetime, and percent remaining, plus a decay curve chart plotting the exponential drop-off with your solved point marked. Every step of the calculation, including any logarithms needed, is shown clearly.
Ideal for chemistry, physics, or nuclear science coursework, it runs entirely in your browser. No sign-up, no downloads, no limits. See the About page or the FAQ for more.
About the Half-Life Calculator
Features
Solve for any variable
N₀, N, t½, or t.
Isotope presets
~15-20 common isotopes auto-fill the known half-life.
Decay constant & mean lifetime
λ and τ computed from the half-life.
Decay curve chart
Plots the exponential curve with the solved point marked.
Frequently Asked Questions
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.