Use the formula: half-life = ln(2) / decay constant
If you know the initial amount and remaining amount, use: remaining amount = initial amount × (1/2)^(time / half-life)
Rearrange to solve for half-life: half-life = time × ln(2) / ln(initial amount / remaining amount)
If the amount halves after a known time interval, that interval is the half-life
For repeated halving, count how many times the quantity is divided by 2 over a measured time and divide the total time by that count