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Half-life calculator

Compute how much of a substance remains after a time, given its half-life.

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Need Amount remaining, Percentage remaining? The Half-life calculator derives it from Initial amount, Half-life, Elapsed time in one step. For instance, with Initial amount = 100, Half-life = 5,730 and Elapsed time = 11,460 it returns Amount remaining = 25 and Percentage remaining = 25%.

How to use it

  1. Enter your values: Initial amount, Half-life, Elapsed time.
  2. Read the result instantly: Amount remaining, Percentage remaining.

Frequently asked questions

What does the Half-life calculator actually compute?

It takes Initial amount, Half-life and Elapsed time and derives Amount remaining and Percentage remaining from them. The calculation is live as you type, so the result updates on every change.

What information do I need to provide?

3 values: Initial amount, Half-life and Elapsed time. Nothing else is required — no account, no file upload.

Can you show a worked example?

With Initial amount = 100, Half-life = 5,730 and Elapsed time = 11,460, the calculator returns Amount remaining = 25 and Percentage remaining = 25%. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

What happens if I enter larger values?

It moves a lot. Using Initial amount = 200, Half-life = 11,460 and Elapsed time = 22,920 instead, Amount remaining goes from 25 to 50 — which is why it is worth testing a few scenarios rather than trusting a single figure.

What does it give for smaller values?

Scaled down to Initial amount = 50, Half-life = 2,865 and Elapsed time = 5,730, Amount remaining comes out at 12.5. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Preparing a solution at a stated concentration, working out how much of a reagent a reaction needs, and converting between mass, moles and volume.

What is the most common mistake?

Confusing molarity with molality. One is per litre of solution and the other per kilogram of solvent; they diverge as concentration rises, and only one of them is temperature-independent.

What is the difference between the Half-life calculator and the Caffeine Half-Life Tracker?

This one returns Amount remaining and Percentage remaining; the Caffeine Half-Life Tracker returns Result. That is the whole difference — open the one whose figure you need.

Where do the figures come from, and how current are they?

Atomic masses are the IUPAC standard values. Results assume ideal behaviour and standard conditions unless the tool says otherwise — real solutions deviate, and lab work needs lab measurement.

Further reading

All guides →
ExplainerHow Half-Life Works: What Is Left After 1, 3 and 10 Half-LivesOne half-life leaves 50%, three leave 12.5%, ten leave less than a tenth of a percent. The formula is a single line — the part worth understanding is why the answer never reaches zero.ExplainerThe Ideal Gas Law Explained: PV = nRT, R in Every Unit, and Where It BreaksPV = nRT holds when the gas is dilute and far from condensing. The value of R depends entirely on the units you feed it, and the temperature is never in degrees Celsius.ExplainerCaffeine Half-Life: Why Your Afternoon Coffee Is Still There at MidnightCaffeine leaves by first-order kinetics, so what remains is the dose times one half to the power of elapsed time over half-life. The half-life is not a constant — it varies by multiples between people, and that is the whole story.How-toHow to Calculate a Dilution with C1V1 = C2V2Solve for the missing term, then convert the answer into a bench instruction. The step almost everyone skips is that the solvent you add is V2 minus V1, not V2.How-toHow to Solve Stoichiometry Problems: Grams to Moles to Ratio to GramsEvery problem in the chapter is the same four moves. The mole ratio is the hinge, and it is the step students lose — worked here end to end, limiting reactant and percent yield included.How-toHow to Calculate Molar Mass, Including Parentheses and HydratesMultiply each atomic weight by its subscript and add. The only three places the arithmetic goes wrong are a subscript after a closing bracket, the hydrate dot, and a capital letter typed as a lowercase one.