Asymptotic distribution of the mean survival time based on the Kaplan–Meier curve with an extrapolated ‘tail’ is derived. A closed formula of the variance estimate is provided. Asymptotic properties of the estimator were studied in a simulation study, which showed that this estimator was unbiased with proper coverage probability and followed a normal distribution. An example is used to demonstrate the application of this estimator. Copyright © 2012 John Wiley & Sons, Ltd.