Half-Life Calculator
Find the amount remaining after exponential decay with a constant half-life.
Formula
N = N₀ × 2^(−t/T½)
Elapsed time: 20 d · Half-life: 10 d · Remaining amount ≈ (100)×(0.25) · Remaining percentage ≈ 100×(0.25)
How to use
- Enter the initial amount in any consistent unit.
- Enter elapsed time and the positive half-life.
- Read the remaining amount and percentage.
Examples
- 100 units with a 10-day half-life leaves 25 after 20 days.
Frequently asked questions
What remains after two half-lives?
One quarter of the initial amount.
Which unit is the result?
The same unit as the initial amount, such as grams or a count.
Does this include decay products?
No. It tracks only the original decaying population with no replenishment.
Sources
Updated: