I have a function that looks like a sigmoid curve. I would like to calculate the right integration border with which the area under the sigmoid curve amounts to a certain value. my curve: model=(3.70288 E^(-((0.134844 (30.8 - 17.8731 t)^2)/t)))/Sqrt[t] I tried: Solve[Integrate[model == 10^-2, {t, 0, x}], x] But that didn't work. Thanks in advance.