Identify the initial amount, concentration, or activity
Determine the amount, concentration, or activity at a later time
Find the time interval between the two measurements
Calculate the fraction remaining: final amount รท initial amount
Use the half-life relationship if the amount is reduced by half each interval
For exponential decay, use the formula (N = N_0 left(frac{1}{2}right)^{t/t_{1/2}})
Rearrange to solve for half-life: (t_{1/2} = frac{t ln 2}{ln(N_0/N)})
If using two data points, compute the decay constant: (k = frac{ln(N_0/N)}{t})
Convert decay constant to half-life: (t_{1/2} = frac{ln 2}{k})
Verify the result using additional measurements if available