The mineral zircon is widely used to determine the age of rocks based on the radioactive decay of U to Pb, but the measured U–Pb date can be too young if the zircon loses Pb. We present a method for estimating the distribution of apparent Pb loss by mathematical convolution. Applying this approach to 10 samples illustrates contrasting patterns of apparent Pb loss. This study highlights the importance of quantifying Pb loss to better understand its potential effects on zircon U–Pb dates.