Half Life Table: Quantity remaining by Initial quantity
Reference table of quantity remaining for Half Life across a range of initial quantity values — exact, engine-computed figures you can read off at a glance.
Half Life Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
Quantity remaining
25.0000
- Number of half-lives
- 2.00
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Half Life Calculator
The Half Life Calculator works out your quantity remaining, along with 1 related figure in an instant. Enter initial quantity, half-life and elapsed time and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.
- Enter the initial quantity.
- Enter the half-life.
- Enter the elapsed time.
- Read off your quantity remaining, together with number of half-lives — the calculator updates automatically, with no button to press.
Formula
The Half Life Calculator uses the formula:
Quantity remaining = Initial quantity × (0.5)^(Elapsed time ÷ Half-life)
Worked example
For example, with initial quantity of 100, half-life of 5 and elapsed time of 10, the quantity remaining is 25.0000.
| Initial quantity | 100 |
|---|---|
| Half-life | 5 |
| Elapsed time | 10 |
| Quantity remaining | 25.0000 |
|---|---|
| Number of half-lives | 2.00 |
Results are estimates for educational use, not professional advice.
Frequently asked questions
Use N = N₀ × (½)^(time ÷ half-life). Starting with 100 over 10 units with a 5-unit half-life leaves 25, after two half-lives.
It is the time for a quantity to fall to half its value. After each half-life, half of what remained is gone.
In radioactivity, medicine (drug clearance), carbon dating and any process with exponential decay.
After about 10 half-lives, less than 0.1% remains, which is often treated as effectively gone.
Enter the initial quantity. Enter the half-life. Enter the elapsed time. Read off your quantity remaining, together with number of half-lives — the calculator updates automatically, with no button to press.
Related guides
How to Calculate Half Life: Formula, Steps & Examples
Learn how to calculate Half Life — the formula explained step by step, with worked examples and a free calculator to check your answer.